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 $182.83   10.379%   $201.8059   $201.81   $201.80   $201.80  
  Purchase #2 $223.53   12.356%   $251.1494   $251.15   $251.15   $251.10  
  Purchase #3 $109.26   8.523%   $118.5722   $118.57   $118.55   $118.60  
  Purchase #4 $158.93   6.827%   $169.7802   $169.78   $169.80   $169.80  
  Purchase #5 $216.63   3.192%   $223.5448   $223.54   $223.55   $223.50  
  Purchase #6 $130.67   4.539%   $136.6011   $136.60   $136.60   $136.60  
  Purchase #7 $223.82   7.578%   $240.7811   $240.78   $240.80   $240.80  
  7 purchase totals = $1,245.67       $1,342.2347   $1,342.23   $1,342.25   $1,342.20