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 $62.47   11.794%   $69.8377   $69.84   $69.85   $69.80  
  Purchase #2 $93.43   12.860%   $105.4451   $105.45   $105.45   $105.40  
  Purchase #3 $242.41   5.386%   $255.4662   $255.47   $255.45   $255.50  
  Purchase #4 $58.48   8.683%   $63.5578   $63.56   $63.55   $63.60  
  Purchase #5 $75.27   9.221%   $82.2106   $82.21   $82.20   $82.20  
  Purchase #6 $191.92   12.211%   $215.3554   $215.36   $215.35   $215.40  
  Purchase #7 $192.39   7.147%   $206.1401   $206.14   $206.15   $206.10  
  7 purchase totals = $916.37       $998.0129   $998.03   $998.00   $998.00