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 $50.26   4.341%   $52.4418   $52.44   $52.45   $52.40  
  Purchase #2 $144.77   13.531%   $164.3588   $164.36   $164.35   $164.40  
  Purchase #3 $154.53   5.486%   $163.0075   $163.01   $163.00   $163.00  
  Purchase #4 $108.84   13.357%   $123.3778   $123.38   $123.40   $123.40  
  Purchase #5 $197.70   4.552%   $206.6993   $206.70   $206.70   $206.70  
  Purchase #6 $197.70   10.559%   $218.5751   $218.58   $218.60   $218.60  
  Purchase #7 $54.32   8.815%   $59.1083   $59.11   $59.10   $59.10  
  7 purchase totals = $908.12       $987.5686   $987.58   $987.60   $987.60