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 $64.37   5.594%   $67.9709   $67.97   $67.95   $68.00  
  Purchase #2 $183.33   10.188%   $202.0077   $202.01   $202.00   $202.00  
  Purchase #3 $228.38   5.265%   $240.4042   $240.40   $240.40   $240.40  
  Purchase #4 $118.61   11.671%   $132.453   $132.45   $132.45   $132.50  
  Purchase #5 $117.55   3.482%   $121.6431   $121.64   $121.65   $121.60  
  Purchase #6 $69.36   8.643%   $75.3548   $75.35   $75.35   $75.40  
  Purchase #7 $142.54   9.851%   $156.5816   $156.58   $156.60   $156.60  
  7 purchase totals = $924.14       $996.4153   $996.40   $996.40   $996.50