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 $184.71   6.688%   $197.0634   $197.06   $197.05   $197.10  
  Purchase #2 $204.73   10.371%   $225.9625   $225.96   $225.95   $226.00  
  Purchase #3 $92.31   3.324%   $95.3784   $95.38   $95.40   $95.40  
  Purchase #4 $54.58   11.275%   $60.7339   $60.73   $60.75   $60.70  
  Purchase #5 $149.49   10.115%   $164.6109   $164.61   $164.60   $164.60  
  Purchase #6 $117.39   13.181%   $132.8632   $132.86   $132.85   $132.90  
  Purchase #7 $153.84   10.468%   $169.944   $169.94   $169.95   $169.90  
  7 purchase totals = $957.05       $1,046.5563   $1,046.54   $1,046.55   $1,046.60