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 $60.75   4.258%   $63.3367   $63.34   $63.35   $63.30  
  Purchase #2 $204.83   5.359%   $215.8068   $215.81   $215.80   $215.80  
  Purchase #3 $118.30   7.462%   $127.1275   $127.13   $127.15   $127.10  
  Purchase #4 $48.37   3.147%   $49.8922   $49.89   $49.90   $49.90  
  Purchase #5 $189.84   6.777%   $202.7055   $202.71   $202.70   $202.70  
  Purchase #6 $157.34   3.513%   $162.8674   $162.87   $162.85   $162.90  
  Purchase #7 $243.92   13.590%   $277.0687   $277.07   $277.05   $277.10  
  7 purchase totals = $1,023.35       $1,098.8048   $1,098.82   $1,098.80   $1,098.80