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 $117.44   6.228%   $124.7542   $124.75   $124.75   $124.80  
  Purchase #2 $50.99   11.542%   $56.8753   $56.88   $56.90   $56.90  
  Purchase #3 $173.56   6.121%   $184.1836   $184.18   $184.20   $184.20  
  Purchase #4 $92.50   4.702%   $96.8494   $96.85   $96.85   $96.80  
  Purchase #5 $217.50   9.249%   $237.6166   $237.62   $237.60   $237.60  
  Purchase #6 $38.91   3.175%   $40.1454   $40.15   $40.15   $40.10  
  Purchase #7 $168.38   13.504%   $191.118   $191.12   $191.10   $191.10  
  7 purchase totals = $859.28       $931.5425   $931.55   $931.55   $931.50