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 $56.96   11.741%   $63.6477   $63.65   $63.65   $63.60  
  Purchase #2 $221.85   12.368%   $249.2884   $249.29   $249.30   $249.30  
  Purchase #3 $63.44   3.785%   $65.8412   $65.84   $65.85   $65.80  
  Purchase #4 $167.64   10.440%   $185.1416   $185.14   $185.15   $185.10  
  Purchase #5 $14.33   11.354%   $15.957   $15.96   $15.95   $16.00  
  Purchase #6 $92.48   6.820%   $98.7871   $98.79   $98.80   $98.80  
  Purchase #7 $67.73   3.263%   $69.94   $69.94   $69.95   $69.90  
  7 purchase totals = $684.43       $748.6030   $748.61   $748.65   $748.50