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 $241.75   13.458%   $274.2847   $274.28   $274.30   $274.30  
  Purchase #2 $36.81   6.223%   $39.1007   $39.10   $39.10   $39.10  
  Purchase #3 $152.47   13.251%   $172.6738   $172.67   $172.65   $172.70  
  Purchase #4 $159.36   10.722%   $176.4466   $176.45   $176.45   $176.40  
  Purchase #5 $138.73   11.438%   $154.5979   $154.60   $154.60   $154.60  
  Purchase #6 $184.27   5.692%   $194.7586   $194.76   $194.75   $194.80  
  Purchase #7 $159.75   6.645%   $170.3654   $170.37   $170.35   $170.40  
  7 purchase totals = $1,073.14       $1,182.2277   $1,182.23   $1,182.20   $1,182.30