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 $141.88   6.447%   $151.027   $151.03   $151.05   $151.00  
  Purchase #2 $245.29   7.838%   $264.5158   $264.52   $264.50   $264.50  
  Purchase #3 $127.63   4.506%   $133.381   $133.38   $133.40   $133.40  
  Purchase #4 $45.70   7.344%   $49.0562   $49.06   $49.05   $49.10  
  Purchase #5 $67.30   11.770%   $75.2212   $75.22   $75.20   $75.20  
  Purchase #6 $185.93   12.401%   $208.9872   $208.99   $209.00   $209.00  
  Purchase #7 $82.73   5.686%   $87.434   $87.43   $87.45   $87.40  
  7 purchase totals = $896.46       $969.6224   $969.63   $969.65   $969.60