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 $60.56   4.795%   $63.4639   $63.46   $63.45   $63.50  
  Purchase #2 $196.57   5.168%   $206.7287   $206.73   $206.75   $206.70  
  Purchase #3 $58.30   9.471%   $63.8216   $63.82   $63.80   $63.80  
  Purchase #4 $12.89   10.156%   $14.1991   $14.20   $14.20   $14.20  
  Purchase #5 $194.77   12.537%   $219.1883   $219.19   $219.20   $219.20  
  Purchase #6 $90.90   6.817%   $97.0967   $97.10   $97.10   $97.10  
  Purchase #7 $70.71   9.618%   $77.5109   $77.51   $77.50   $77.50  
  7 purchase totals = $684.70       $742.0092   $742.01   $742.00   $742.00