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   8.362%   $63.5001   $63.50   $63.50   $63.50  
  Purchase #2 $22.45   7.763%   $24.1928   $24.19   $24.20   $24.20  
  Purchase #3 $199.61   7.229%   $214.0398   $214.04   $214.05   $214.00  
  Purchase #4 $90.48   8.454%   $98.1292   $98.13   $98.15   $98.10  
  Purchase #5 $163.31   13.870%   $185.9611   $185.96   $185.95   $186.00  
  Purchase #6 $197.53   4.258%   $205.9408   $205.94   $205.95   $205.90  
  Purchase #7 $12.74   7.607%   $13.7091   $13.71   $13.70   $13.70  
  7 purchase totals = $744.72       $805.4729   $805.47   $805.50   $805.40