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 $163.69   11.773%   $182.9612   $182.96   $182.95   $183.00  
  Purchase #2 $52.32   8.736%   $56.8907   $56.89   $56.90   $56.90  
  Purchase #3 $106.51   12.470%   $119.7918   $119.79   $119.80   $119.80  
  Purchase #4 $181.36   11.188%   $201.6506   $201.65   $201.65   $201.70  
  Purchase #5 $50.34   9.557%   $55.151   $55.15   $55.15   $55.20  
  Purchase #6 $104.29   7.711%   $112.3318   $112.33   $112.35   $112.30  
  Purchase #7 $173.42   11.491%   $193.3477   $193.35   $193.35   $193.30  
  7 purchase totals = $831.93       $922.1248   $922.12   $922.15   $922.20