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 $207.94   12.777%   $234.5085   $234.51   $234.50   $234.50  
  Purchase #2 $101.48   13.826%   $115.5106   $115.51   $115.50   $115.50  
  Purchase #3 $44.37   3.676%   $46.001   $46.00   $46.00   $46.00  
  Purchase #4 $153.77   7.156%   $164.7738   $164.77   $164.75   $164.80  
  Purchase #5 $33.60   8.293%   $36.3864   $36.39   $36.40   $36.40  
  Purchase #6 $112.48   11.253%   $125.1374   $125.14   $125.15   $125.10  
  Purchase #7 $75.46   7.359%   $81.0131   $81.01   $81.00   $81.00  
  7 purchase totals = $729.10       $803.3308   $803.33   $803.30   $803.30