Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $248.95   10.850%   $275.9611   $275.96   $275.95   $276.00  
  Purchase #2 $166.41   9.701%   $182.5534   $182.55   $182.55   $182.60  
  Purchase #3 $219.34   7.669%   $236.1612   $236.16   $236.15   $236.20  
  Purchase #4 $127.57   11.791%   $142.6118   $142.61   $142.60   $142.60  
  Purchase #5 $227.56   10.684%   $251.8725   $251.87   $251.85   $251.90  
  Purchase #6 $162.34   7.791%   $174.9879   $174.99   $175.00   $175.00  
  Purchase #7 $205.29   3.562%   $212.6024   $212.60   $212.60   $212.60  
  7 purchase totals = $1,357.46       $1,476.7503   $1,476.74   $1,476.70   $1,476.90