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 $219.96   9.558%   $240.9838   $240.98   $241.00   $241.00  
  Purchase #2 $175.75   10.287%   $193.8294   $193.83   $193.85   $193.80  
  Purchase #3 $107.90   8.806%   $117.4017   $117.40   $117.40   $117.40  
  Purchase #4 $172.28   13.739%   $195.9495   $195.95   $195.95   $195.90  
  Purchase #5 $233.58   4.701%   $244.5606   $244.56   $244.55   $244.60  
  Purchase #6 $104.59   7.646%   $112.587   $112.59   $112.60   $112.60  
  Purchase #7 $178.38   13.743%   $202.8948   $202.89   $202.90   $202.90  
  7 purchase totals = $1,192.44       $1,308.2068   $1,308.20   $1,308.25   $1,308.20