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 $125.53   8.327%   $135.9829   $135.98   $136.00   $136.00  
  Purchase #2 $5.88   5.269%   $6.1898   $6.19   $6.20   $6.20  
  Purchase #3 $215.51   6.707%   $229.9643   $229.96   $229.95   $230.00  
  Purchase #4 $111.44   4.752%   $116.7356   $116.74   $116.75   $116.70  
  Purchase #5 $61.59   6.450%   $65.5626   $65.56   $65.55   $65.60  
  Purchase #6 $223.48   4.865%   $234.3523   $234.35   $234.35   $234.40  
  Purchase #7 $39.28   3.218%   $40.544   $40.54   $40.55   $40.50  
  7 purchase totals = $782.71       $829.3315   $829.32   $829.35   $829.40