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 $88.70   4.377%   $92.5824   $92.58   $92.60   $92.60  
  Purchase #2 $216.77   11.344%   $241.3604   $241.36   $241.35   $241.40  
  Purchase #3 $48.44   13.333%   $54.8985   $54.90   $54.90   $54.90  
  Purchase #4 $102.38   5.773%   $108.2904   $108.29   $108.30   $108.30  
  Purchase #5 $199.66   4.301%   $208.2474   $208.25   $208.25   $208.20  
  Purchase #6 $64.33   8.740%   $69.9524   $69.95   $69.95   $70.00  
  Purchase #7 $196.81   10.365%   $217.2094   $217.21   $217.20   $217.20  
  7 purchase totals = $917.09       $992.5409   $992.54   $992.55   $992.60