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 $86.52   11.277%   $96.2769   $96.28   $96.30   $96.30  
  Purchase #2 $247.41   5.834%   $261.8439   $261.84   $261.85   $261.80  
  Purchase #3 $85.55   8.179%   $92.5471   $92.55   $92.55   $92.50  
  Purchase #4 $12.74   6.306%   $13.5434   $13.54   $13.55   $13.50  
  Purchase #5 $137.91   10.195%   $151.9699   $151.97   $151.95   $152.00  
  Purchase #6 $219.89   12.344%   $247.0332   $247.03   $247.05   $247.00  
  Purchase #7 $98.90   9.152%   $107.9513   $107.95   $107.95   $108.00  
  7 purchase totals = $888.92       $971.1657   $971.16   $971.20   $971.10