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 $60.34   13.471%   $68.4684   $68.47   $68.45   $68.50  
  Purchase #2 $208.43   10.365%   $230.0338   $230.03   $230.05   $230.00  
  Purchase #3 $51.53   7.390%   $55.3381   $55.34   $55.35   $55.30  
  Purchase #4 $132.82   6.146%   $140.9831   $140.98   $141.00   $141.00  
  Purchase #5 $213.30   8.726%   $231.9126   $231.91   $231.90   $231.90  
  Purchase #6 $109.38   3.300%   $112.9895   $112.99   $113.00   $113.00  
  Purchase #7 $82.80   7.523%   $89.029   $89.03   $89.05   $89.00  
  7 purchase totals = $858.60       $928.7545   $928.75   $928.80   $928.70