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 $87.80   12.459%   $98.739   $98.74   $98.75   $98.70  
  Purchase #2 $178.27   6.381%   $189.6454   $189.65   $189.65   $189.60  
  Purchase #3 $234.40   3.751%   $243.1923   $243.19   $243.20   $243.20  
  Purchase #4 $119.58   5.147%   $125.7348   $125.73   $125.75   $125.70  
  Purchase #5 $189.68   13.823%   $215.8995   $215.90   $215.90   $215.90  
  Purchase #6 $89.50   4.700%   $93.7065   $93.71   $93.70   $93.70  
  Purchase #7 $95.43   3.145%   $98.4313   $98.43   $98.45   $98.40  
  7 purchase totals = $994.66       $1,065.3488   $1,065.35   $1,065.40   $1,065.20