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 $243.76   9.838%   $267.7411   $267.74   $267.75   $267.70  
  Purchase #2 $220.80   3.141%   $227.7353   $227.74   $227.75   $227.70  
  Purchase #3 $119.48   10.256%   $131.7339   $131.73   $131.75   $131.70  
  Purchase #4 $155.35   12.439%   $174.674   $174.67   $174.65   $174.70  
  Purchase #5 $232.86   7.717%   $250.8298   $250.83   $250.85   $250.80  
  Purchase #6 $119.52   6.634%   $127.449   $127.45   $127.45   $127.40  
  Purchase #7 $246.67   8.844%   $268.4855   $268.49   $268.50   $268.50  
  7 purchase totals = $1,338.44       $1,448.6486   $1,448.65   $1,448.70   $1,448.50