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 $75.98   8.243%   $82.243   $82.24   $82.25   $82.20  
  Purchase #2 $178.76   8.457%   $193.8777   $193.88   $193.90   $193.90  
  Purchase #3 $207.86   4.686%   $217.6003   $217.60   $217.60   $217.60  
  Purchase #4 $90.68   10.290%   $100.011   $100.01   $100.00   $100.00  
  Purchase #5 $100.54   3.410%   $103.9684   $103.97   $103.95   $104.00  
  Purchase #6 $25.80   6.195%   $27.3983   $27.40   $27.40   $27.40  
  Purchase #7 $176.76   13.692%   $200.962   $200.96   $200.95   $201.00  
  7 purchase totals = $856.38       $926.0607   $926.06   $926.05   $926.10