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 $45.51   9.866%   $50   $50.00   $50.00   $50.00  
  Purchase #2 $136.69   3.699%   $141.7462   $141.75   $141.75   $141.70  
  Purchase #3 $194.95   5.612%   $205.8906   $205.89   $205.90   $205.90  
  Purchase #4 $218.54   10.433%   $241.3403   $241.34   $241.35   $241.30  
  Purchase #5 $243.69   13.298%   $276.0959   $276.10   $276.10   $276.10  
  Purchase #6 $140.51   5.448%   $148.165   $148.17   $148.15   $148.20  
  Purchase #7 $199.62   11.244%   $222.0653   $222.07   $222.05   $222.10  
  7 purchase totals = $1,179.51       $1,285.3033   $1,285.32   $1,285.30   $1,285.30