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 $218.45   11.601%   $243.7924   $243.79   $243.80   $243.80  
  Purchase #2 $157.84   11.501%   $175.9932   $175.99   $176.00   $176.00  
  Purchase #3 $62.25   4.861%   $65.276   $65.28   $65.30   $65.30  
  Purchase #4 $193.84   5.149%   $203.8208   $203.82   $203.80   $203.80  
  Purchase #5 $159.27   8.790%   $173.2698   $173.27   $173.25   $173.30  
  Purchase #6 $215.40   10.400%   $237.8016   $237.80   $237.80   $237.80  
  Purchase #7 $164.74   12.102%   $184.6768   $184.68   $184.70   $184.70  
  7 purchase totals = $1,171.79       $1,284.6306   $1,284.63   $1,284.65   $1,284.70