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 $232.57   7.374%   $249.7197   $249.72   $249.70   $249.70  
  Purchase #2 $117.33   6.124%   $124.5153   $124.52   $124.50   $124.50  
  Purchase #3 $34.40   6.827%   $36.7485   $36.75   $36.75   $36.70  
  Purchase #4 $216.47   4.157%   $225.4687   $225.47   $225.45   $225.50  
  Purchase #5 $128.59   3.190%   $132.692   $132.69   $132.70   $132.70  
  Purchase #6 $7.27   4.690%   $7.611   $7.61   $7.60   $7.60  
  Purchase #7 $176.53   3.271%   $182.3043   $182.30   $182.30   $182.30  
  7 purchase totals = $913.16       $959.0595   $959.06   $959.00   $959.00