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 $60.57   6.626%   $64.5834   $64.58   $64.60   $64.60  
  Purchase #2 $49.78   8.804%   $54.1626   $54.16   $54.15   $54.20  
  Purchase #3 $53.80   5.214%   $56.6051   $56.61   $56.60   $56.60  
  Purchase #4 $195.97   4.596%   $204.9768   $204.98   $205.00   $205.00  
  Purchase #5 $221.81   4.842%   $232.55   $232.55   $232.55   $232.60  
  Purchase #6 $31.78   7.129%   $34.0456   $34.05   $34.05   $34.00  
  Purchase #7 $161.62   12.735%   $182.2023   $182.20   $182.20   $182.20  
  7 purchase totals = $775.33       $829.1258   $829.13   $829.15   $829.20