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 $68.62   9.480%   $75.1252   $75.13   $75.15   $75.10  
  Purchase #2 $7.92   8.821%   $8.6186   $8.62   $8.60   $8.60  
  Purchase #3 $110.97   6.290%   $117.95   $117.95   $117.95   $118.00  
  Purchase #4 $183.75   9.813%   $201.7814   $201.78   $201.80   $201.80  
  Purchase #5 $69.26   10.844%   $76.7706   $76.77   $76.75   $76.80  
  Purchase #6 $250.33   10.734%   $277.2004   $277.20   $277.20   $277.20  
  Purchase #7 $207.44   4.454%   $216.6794   $216.68   $216.70   $216.70  
  7 purchase totals = $898.29       $974.1256   $974.13   $974.15   $974.20