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 $66.53   13.228%   $75.3306   $75.33   $75.35   $75.30  
  Purchase #2 $238.51   13.748%   $271.3004   $271.30   $271.30   $271.30  
  Purchase #3 $67.84   3.179%   $69.9966   $70.00   $70.00   $70.00  
  Purchase #4 $167.44   13.151%   $189.46   $189.46   $189.45   $189.50  
  Purchase #5 $50.59   4.659%   $52.947   $52.95   $52.95   $52.90  
  Purchase #6 $76.82   13.684%   $87.332   $87.33   $87.35   $87.30  
  Purchase #7 $81.32   7.614%   $87.5117   $87.51   $87.50   $87.50  
  7 purchase totals = $749.05       $833.8783   $833.88   $833.90   $833.80