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 $191.94   3.723%   $199.0859   $199.09   $199.10   $199.10  
  Purchase #2 $138.42   3.503%   $143.2689   $143.27   $143.25   $143.30  
  Purchase #3 $44.32   11.288%   $49.3228   $49.32   $49.30   $49.30  
  Purchase #4 $87.96   5.264%   $92.5902   $92.59   $92.60   $92.60  
  Purchase #5 $214.74   7.178%   $230.154   $230.15   $230.15   $230.20  
  Purchase #6 $164.92   5.130%   $173.3804   $173.38   $173.40   $173.40  
  Purchase #7 $68.65   11.470%   $76.5242   $76.52   $76.50   $76.50  
  7 purchase totals = $910.95       $964.3264   $964.32   $964.30   $964.40