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 $86.78   6.552%   $92.4658   $92.47   $92.45   $92.50  
  Purchase #2 $156.76   11.322%   $174.5084   $174.51   $174.50   $174.50  
  Purchase #3 $49.29   4.770%   $51.6411   $51.64   $51.65   $51.60  
  Purchase #4 $76.77   10.495%   $84.827   $84.83   $84.85   $84.80  
  Purchase #5 $244.73   6.367%   $260.312   $260.31   $260.30   $260.30  
  Purchase #6 $232.41   10.782%   $257.4684   $257.47   $257.45   $257.50  
  Purchase #7 $239.25   8.843%   $260.4069   $260.41   $260.40   $260.40  
  7 purchase totals = $1,085.99       $1,181.6296   $1,181.64   $1,181.60   $1,181.60