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 $52.46   9.845%   $57.6247   $57.62   $57.60   $57.60  
  Purchase #2 $215.51   12.208%   $241.8195   $241.82   $241.80   $241.80  
  Purchase #3 $12.45   11.852%   $13.9256   $13.93   $13.95   $13.90  
  Purchase #4 $128.42   3.669%   $133.1317   $133.13   $133.15   $133.10  
  Purchase #5 $154.88   11.317%   $172.4078   $172.41   $172.40   $172.40  
  Purchase #6 $68.85   11.731%   $76.9268   $76.93   $76.95   $76.90  
  Purchase #7 $172.98   13.285%   $195.9604   $195.96   $195.95   $196.00  
  7 purchase totals = $805.55       $891.7965   $891.80   $891.80   $891.70