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 $37.34   10.194%   $41.1464   $41.15   $41.15   $41.10  
  Purchase #2 $239.48   6.866%   $255.9227   $255.92   $255.90   $255.90  
  Purchase #3 $159.90   8.186%   $172.9894   $172.99   $173.00   $173.00  
  Purchase #4 $57.57   3.625%   $59.6569   $59.66   $59.65   $59.70  
  Purchase #5 $200.54   5.319%   $211.2067   $211.21   $211.20   $211.20  
  Purchase #6 $16.94   3.859%   $17.5937   $17.59   $17.60   $17.60  
  Purchase #7 $89.39   7.368%   $95.9763   $95.98   $96.00   $96.00  
  7 purchase totals = $801.16       $854.4921   $854.50   $854.50   $854.50