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 $46.62   8.557%   $50.6093   $50.61   $50.60   $50.60  
  Purchase #2 $134.27   8.440%   $145.6024   $145.60   $145.60   $145.60  
  Purchase #3 $156.28   13.294%   $177.0559   $177.06   $177.05   $177.10  
  Purchase #4 $86.46   7.496%   $92.941   $92.94   $92.95   $92.90  
  Purchase #5 $137.74   10.465%   $152.1545   $152.15   $152.15   $152.20  
  Purchase #6 $133.53   5.118%   $140.3641   $140.36   $140.35   $140.40  
  Purchase #7 $56.26   11.287%   $62.6101   $62.61   $62.60   $62.60  
  7 purchase totals = $751.16       $821.3373   $821.33   $821.30   $821.40