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 $216.32   11.713%   $241.6576   $241.66   $241.65   $241.70  
  Purchase #2 $199.98   5.668%   $211.3149   $211.31   $211.30   $211.30  
  Purchase #3 $26.30   5.390%   $27.7176   $27.72   $27.70   $27.70  
  Purchase #4 $85.39   12.402%   $95.9801   $95.98   $96.00   $96.00  
  Purchase #5 $99.71   7.403%   $107.0915   $107.09   $107.10   $107.10  
  Purchase #6 $18.36   11.719%   $20.5116   $20.51   $20.50   $20.50  
  Purchase #7 $17.50   12.772%   $19.7351   $19.74   $19.75   $19.70  
  7 purchase totals = $663.56       $724.0084   $724.01   $724.00   $724.00