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 $64.51   6.427%   $68.6561   $68.66   $68.65   $68.70  
  Purchase #2 $176.94   13.206%   $200.3067   $200.31   $200.30   $200.30  
  Purchase #3 $98.30   10.865%   $108.9803   $108.98   $109.00   $109.00  
  Purchase #4 $108.31   7.347%   $116.2675   $116.27   $116.25   $116.30  
  Purchase #5 $144.36   12.855%   $162.9175   $162.92   $162.90   $162.90  
  Purchase #6 $237.43   8.416%   $257.4121   $257.41   $257.40   $257.40  
  Purchase #7 $131.65   7.819%   $141.9437   $141.94   $141.95   $141.90  
  7 purchase totals = $961.50       $1,056.4839   $1,056.49   $1,056.45   $1,056.50