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 $119.85   13.395%   $135.9039   $135.90   $135.90   $135.90  
  Purchase #2 $205.40   4.815%   $215.29   $215.29   $215.30   $215.30  
  Purchase #3 $16.44   5.190%   $17.2932   $17.29   $17.30   $17.30  
  Purchase #4 $152.53   4.234%   $158.9881   $158.99   $159.00   $159.00  
  Purchase #5 $209.62   11.706%   $234.1581   $234.16   $234.15   $234.20  
  Purchase #6 $120.94   9.736%   $132.7147   $132.71   $132.70   $132.70  
  Purchase #7 $52.71   9.220%   $57.5699   $57.57   $57.55   $57.60  
  7 purchase totals = $877.49       $951.9179   $951.91   $951.90   $952.00