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 $112.42   4.750%   $117.76   $117.76   $117.75   $117.80  
  Purchase #2 $244.73   11.527%   $272.94   $272.94   $272.95   $272.90  
  Purchase #3 $5.84   8.380%   $6.3294   $6.33   $6.35   $6.30  
  Purchase #4 $226.92   6.355%   $241.3408   $241.34   $241.35   $241.30  
  Purchase #5 $145.75   5.726%   $154.0956   $154.10   $154.10   $154.10  
  Purchase #6 $59.70   13.406%   $67.7034   $67.70   $67.70   $67.70  
  Purchase #7 $116.92   7.437%   $125.6153   $125.62   $125.60   $125.60  
  7 purchase totals = $912.28       $985.7845   $985.79   $985.80   $985.70