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 $113.99   3.520%   $118.0024   $118.00   $118.00   $118.00  
  Purchase #2 $92.62   12.118%   $103.8437   $103.84   $103.85   $103.80  
  Purchase #3 $179.41   11.282%   $199.651   $199.65   $199.65   $199.70  
  Purchase #4 $155.85   8.620%   $169.2843   $169.28   $169.30   $169.30  
  Purchase #5 $218.67   9.814%   $240.1303   $240.13   $240.15   $240.10  
  Purchase #6 $250.86   4.513%   $262.1813   $262.18   $262.20   $262.20  
  Purchase #7 $95.42   6.480%   $101.6032   $101.60   $101.60   $101.60  
  7 purchase totals = $1,106.82       $1,194.6962   $1,194.68   $1,194.75   $1,194.70