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 $61.94   4.477%   $64.7131   $64.71   $64.70   $64.70  
  Purchase #2 $87.43   6.602%   $93.2021   $93.20   $93.20   $93.20  
  Purchase #3 $99.92   10.322%   $110.2337   $110.23   $110.25   $110.20  
  Purchase #4 $143.63   6.653%   $153.1857   $153.19   $153.20   $153.20  
  Purchase #5 $71.49   5.757%   $75.6057   $75.61   $75.60   $75.60  
  Purchase #6 $45.51   7.673%   $49.002   $49.00   $49.00   $49.00  
  Purchase #7 $152.72   10.389%   $168.5861   $168.59   $168.60   $168.60  
  7 purchase totals = $662.64       $714.5284   $714.53   $714.55   $714.50