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 $186.74   8.205%   $202.062   $202.06   $202.05   $202.10  
  Purchase #2 $244.42   11.180%   $271.7462   $271.75   $271.75   $271.70  
  Purchase #3 $104.33   3.474%   $107.9544   $107.95   $107.95   $108.00  
  Purchase #4 $215.87   11.450%   $240.5871   $240.59   $240.60   $240.60  
  Purchase #5 $158.44   5.245%   $166.7502   $166.75   $166.75   $166.80  
  Purchase #6 $171.71   13.478%   $194.8531   $194.85   $194.85   $194.90  
  Purchase #7 $210.66   13.712%   $239.5457   $239.55   $239.55   $239.50  
  7 purchase totals = $1,292.17       $1,423.4987   $1,423.50   $1,423.50   $1,423.60