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 $53.83   7.669%   $57.9582   $57.96   $57.95   $58.00  
  Purchase #2 $124.96   5.855%   $132.2764   $132.28   $132.30   $132.30  
  Purchase #3 $109.54   9.565%   $120.0175   $120.02   $120.00   $120.00  
  Purchase #4 $231.32   13.623%   $262.8327   $262.83   $262.85   $262.80  
  Purchase #5 $114.49   8.583%   $124.3167   $124.32   $124.30   $124.30  
  Purchase #6 $88.95   4.317%   $92.79   $92.79   $92.80   $92.80  
  Purchase #7 $201.33   5.508%   $212.4193   $212.42   $212.40   $212.40  
  7 purchase totals = $924.42       $1,002.6108   $1,002.62   $1,002.60   $1,002.60