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 $228.72   5.751%   $241.8737   $241.87   $241.85   $241.90  
  Purchase #2 $58.68   13.425%   $66.5578   $66.56   $66.55   $66.60  
  Purchase #3 $31.42   11.769%   $35.1178   $35.12   $35.10   $35.10  
  Purchase #4 $41.85   4.104%   $43.5675   $43.57   $43.55   $43.60  
  Purchase #5 $77.45   5.744%   $81.8987   $81.90   $81.90   $81.90  
  Purchase #6 $121.97   3.363%   $126.0719   $126.07   $126.05   $126.10  
  Purchase #7 $250.76   12.757%   $282.7495   $282.75   $282.75   $282.70  
  7 purchase totals = $810.85       $877.8369   $877.84   $877.75   $877.90