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 $165.69   10.224%   $182.6301   $182.63   $182.65   $182.60  
  Purchase #2 $80.66   5.331%   $84.96   $84.96   $84.95   $85.00  
  Purchase #3 $106.67   8.368%   $115.5961   $115.60   $115.60   $115.60  
  Purchase #4 $108.95   11.609%   $121.598   $121.60   $121.60   $121.60  
  Purchase #5 $133.26   12.734%   $150.2293   $150.23   $150.25   $150.20  
  Purchase #6 $126.42   10.255%   $139.3844   $139.38   $139.40   $139.40  
  Purchase #7 $180.74   12.509%   $203.3488   $203.35   $203.35   $203.30  
  7 purchase totals = $902.39       $997.7467   $997.75   $997.80   $997.70