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 $172.79   13.194%   $195.5879   $195.59   $195.60   $195.60  
  Purchase #2 $191.42   5.861%   $202.6391   $202.64   $202.65   $202.60  
  Purchase #3 $126.98   13.737%   $144.4232   $144.42   $144.40   $144.40  
  Purchase #4 $88.59   7.601%   $95.3237   $95.32   $95.30   $95.30  
  Purchase #5 $169.71   13.634%   $192.8483   $192.85   $192.85   $192.80  
  Purchase #6 $17.72   9.222%   $19.3541   $19.35   $19.35   $19.40  
  Purchase #7 $54.71   9.863%   $60.106   $60.11   $60.10   $60.10  
  7 purchase totals = $821.92       $910.2823   $910.28   $910.25   $910.20