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 $241.60   8.331%   $261.7277   $261.73   $261.75   $261.70  
  Purchase #2 $81.36   4.419%   $84.9553   $84.96   $84.95   $85.00  
  Purchase #3 $82.89   11.407%   $92.3453   $92.35   $92.35   $92.30  
  Purchase #4 $129.63   6.662%   $138.266   $138.27   $138.25   $138.30  
  Purchase #5 $72.46   5.309%   $76.3069   $76.31   $76.30   $76.30  
  Purchase #6 $235.73   13.300%   $267.0821   $267.08   $267.10   $267.10  
  Purchase #7 $51.73   4.107%   $53.8546   $53.85   $53.85   $53.90  
  7 purchase totals = $895.40       $974.5379   $974.55   $974.55   $974.60