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 $177.49   11.214%   $197.3937   $197.39   $197.40   $197.40  
  Purchase #2 $228.87   12.856%   $258.2935   $258.29   $258.30   $258.30  
  Purchase #3 $94.98   4.365%   $99.1259   $99.13   $99.15   $99.10  
  Purchase #4 $71.69   3.188%   $73.9755   $73.98   $74.00   $74.00  
  Purchase #5 $227.75   7.718%   $245.3277   $245.33   $245.35   $245.30  
  Purchase #6 $21.38   13.581%   $24.2836   $24.28   $24.30   $24.30  
  Purchase #7 $112.65   7.537%   $121.1404   $121.14   $121.15   $121.10  
  7 purchase totals = $934.81       $1,019.5403   $1,019.54   $1,019.65   $1,019.50