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 $90.73   6.386%   $96.524   $96.52   $96.50   $96.50  
  Purchase #2 $98.48   3.298%   $101.7279   $101.73   $101.75   $101.70  
  Purchase #3 $227.87   5.328%   $240.0109   $240.01   $240.00   $240.00  
  Purchase #4 $242.61   6.290%   $257.8702   $257.87   $257.85   $257.90  
  Purchase #5 $244.44   9.127%   $266.75   $266.75   $266.75   $266.80  
  Purchase #6 $92.80   10.315%   $102.3723   $102.37   $102.35   $102.40  
  Purchase #7 $138.44   3.485%   $143.2646   $143.26   $143.25   $143.30  
  7 purchase totals = $1,135.37       $1,208.5199   $1,208.51   $1,208.45   $1,208.60