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 $74.64   13.359%   $84.6112   $84.61   $84.60   $84.60  
  Purchase #2 $138.38   8.407%   $150.0136   $150.01   $150.00   $150.00  
  Purchase #3 $124.92   8.526%   $135.5707   $135.57   $135.55   $135.60  
  Purchase #4 $19.77   5.774%   $20.9115   $20.91   $20.90   $20.90  
  Purchase #5 $166.66   11.706%   $186.1692   $186.17   $186.15   $186.20  
  Purchase #6 $76.64   11.129%   $85.1693   $85.17   $85.15   $85.20  
  Purchase #7 $183.70   8.673%   $199.6323   $199.63   $199.65   $199.60  
  7 purchase totals = $784.71       $862.0778   $862.07   $862.00   $862.10