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 $58.60   8.489%   $63.5746   $63.57   $63.55   $63.60  
  Purchase #2 $20.80   11.638%   $23.2207   $23.22   $23.20   $23.20  
  Purchase #3 $106.50   5.707%   $112.578   $112.58   $112.60   $112.60  
  Purchase #4 $133.62   8.356%   $144.7853   $144.79   $144.80   $144.80  
  Purchase #5 $72.75   3.167%   $75.054   $75.05   $75.05   $75.10  
  Purchase #6 $214.99   13.652%   $244.3404   $244.34   $244.35   $244.30  
  Purchase #7 $66.27   4.772%   $69.4324   $69.43   $69.45   $69.40  
  7 purchase totals = $673.53       $732.9854   $732.98   $733.00   $733.00