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 $195.56   4.697%   $204.7455   $204.75   $204.75   $204.70  
  Purchase #2 $95.89   10.394%   $105.8568   $105.86   $105.85   $105.90  
  Purchase #3 $231.28   13.422%   $262.3224   $262.32   $262.30   $262.30  
  Purchase #4 $84.46   11.873%   $94.4879   $94.49   $94.50   $94.50  
  Purchase #5 $143.84   12.553%   $161.8962   $161.90   $161.90   $161.90  
  Purchase #6 $75.86   10.413%   $83.7593   $83.76   $83.75   $83.80  
  Purchase #7 $196.94   9.183%   $215.025   $215.03   $215.05   $215.00  
  7 purchase totals = $1,023.83       $1,128.0931   $1,128.11   $1,128.10   $1,128.10