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 $238.62   6.284%   $253.6149   $253.61   $253.60   $253.60  
  Purchase #2 $59.25   10.634%   $65.5506   $65.55   $65.55   $65.60  
  Purchase #3 $24.48   8.327%   $26.5184   $26.52   $26.50   $26.50  
  Purchase #4 $103.85   9.278%   $113.4852   $113.49   $113.50   $113.50  
  Purchase #5 $223.80   12.361%   $251.4639   $251.46   $251.45   $251.50  
  Purchase #6 $28.71   5.799%   $30.3749   $30.37   $30.35   $30.40  
  Purchase #7 $140.41   10.600%   $155.2935   $155.29   $155.30   $155.30  
  7 purchase totals = $819.12       $896.3014   $896.29   $896.25   $896.40