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 $184.94   11.239%   $205.7254   $205.73   $205.75   $205.70  
  Purchase #2 $116.76   6.663%   $124.5397   $124.54   $124.55   $124.50  
  Purchase #3 $184.55   10.619%   $204.1474   $204.15   $204.15   $204.10  
  Purchase #4 $107.60   5.733%   $113.7687   $113.77   $113.75   $113.80  
  Purchase #5 $191.98   5.182%   $201.9284   $201.93   $201.95   $201.90  
  Purchase #6 $213.93   12.476%   $240.6199   $240.62   $240.60   $240.60  
  Purchase #7 $141.57   6.825%   $151.2322   $151.23   $151.25   $151.20  
  7 purchase totals = $1,141.33       $1,241.9617   $1,241.97   $1,242.00   $1,241.80