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 $104.55   13.791%   $118.9685   $118.97   $118.95   $119.00  
  Purchase #2 $153.28   3.501%   $158.6463   $158.65   $158.65   $158.60  
  Purchase #3 $82.48   3.306%   $85.2068   $85.21   $85.20   $85.20  
  Purchase #4 $208.61   7.649%   $224.5666   $224.57   $224.55   $224.60  
  Purchase #5 $250.95   9.788%   $275.513   $275.51   $275.50   $275.50  
  Purchase #6 $225.92   12.791%   $254.8174   $254.82   $254.80   $254.80  
  Purchase #7 $91.98   12.484%   $103.4628   $103.46   $103.45   $103.50  
  7 purchase totals = $1,117.77       $1,221.1814   $1,221.19   $1,221.10   $1,221.20