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 $247.41   8.657%   $268.8283   $268.83   $268.85   $268.80  
  Purchase #2 $240.84   6.512%   $256.5235   $256.52   $256.50   $256.50  
  Purchase #3 $125.51   8.393%   $136.0441   $136.04   $136.05   $136.00  
  Purchase #4 $44.30   3.781%   $45.975   $45.98   $46.00   $46.00  
  Purchase #5 $229.36   5.674%   $242.3739   $242.37   $242.35   $242.40  
  Purchase #6 $246.92   3.275%   $255.0066   $255.01   $255.00   $255.00  
  Purchase #7 $212.53   13.452%   $241.1195   $241.12   $241.10   $241.10  
  7 purchase totals = $1,346.87       $1,445.8709   $1,445.87   $1,445.85   $1,445.80