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 $44.57   13.378%   $50.5326   $50.53   $50.55   $50.50  
  Purchase #2 $250.95   7.710%   $270.2982   $270.30   $270.30   $270.30  
  Purchase #3 $47.65   10.306%   $52.5608   $52.56   $52.55   $52.60  
  Purchase #4 $154.59   8.201%   $167.2679   $167.27   $167.25   $167.30  
  Purchase #5 $128.54   10.707%   $142.3028   $142.30   $142.30   $142.30  
  Purchase #6 $9.93   5.374%   $10.4636   $10.46   $10.45   $10.50  
  Purchase #7 $83.68   10.203%   $92.2179   $92.22   $92.20   $92.20  
  7 purchase totals = $719.91       $785.6438   $785.64   $785.60   $785.70