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 $191.60   5.413%   $201.9713   $201.97   $201.95   $202.00  
  Purchase #2 $55.77   13.553%   $63.3285   $63.33   $63.35   $63.30  
  Purchase #3 $33.66   6.632%   $35.8923   $35.89   $35.90   $35.90  
  Purchase #4 $158.26   3.383%   $163.6139   $163.61   $163.60   $163.60  
  Purchase #5 $189.87   12.533%   $213.6664   $213.67   $213.65   $213.70  
  Purchase #6 $72.50   9.423%   $79.3317   $79.33   $79.35   $79.30  
  Purchase #7 $213.47   12.567%   $240.2968   $240.30   $240.30   $240.30  
  7 purchase totals = $915.13       $998.1009   $998.10   $998.10   $998.10