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 $90.79   5.578%   $95.8543   $95.85   $95.85   $95.90  
  Purchase #2 $220.78   9.581%   $241.9329   $241.93   $241.95   $241.90  
  Purchase #3 $50.47   10.733%   $55.8869   $55.89   $55.90   $55.90  
  Purchase #4 $82.44   11.317%   $91.7697   $91.77   $91.75   $91.80  
  Purchase #5 $236.91   5.242%   $249.3288   $249.33   $249.35   $249.30  
  Purchase #6 $158.61   11.447%   $176.7661   $176.77   $176.75   $176.80  
  Purchase #7 $140.81   5.250%   $148.2025   $148.20   $148.20   $148.20  
  7 purchase totals = $980.81       $1,059.7412   $1,059.74   $1,059.75   $1,059.80