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 $125.39   13.281%   $142.043   $142.04   $142.05   $142.00  
  Purchase #2 $92.36   5.602%   $97.534   $97.53   $97.55   $97.50  
  Purchase #3 $143.57   10.434%   $158.5501   $158.55   $158.55   $158.60  
  Purchase #4 $217.95   9.188%   $237.9752   $237.98   $238.00   $238.00  
  Purchase #5 $23.99   6.840%   $25.6309   $25.63   $25.65   $25.60  
  Purchase #6 $202.88   5.500%   $214.0384   $214.04   $214.05   $214.00  
  Purchase #7 $172.90   13.433%   $196.1257   $196.13   $196.15   $196.10  
  7 purchase totals = $979.04       $1,071.8973   $1,071.90   $1,072.00   $1,071.80