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 $41.83   5.832%   $44.2695   $44.27   $44.25   $44.30  
  Purchase #2 $67.80   11.773%   $75.7821   $75.78   $75.80   $75.80  
  Purchase #3 $112.76   6.647%   $120.2552   $120.26   $120.25   $120.30  
  Purchase #4 $201.39   6.125%   $213.7251   $213.73   $213.75   $213.70  
  Purchase #5 $184.46   12.175%   $206.918   $206.92   $206.90   $206.90  
  Purchase #6 $16.31   7.178%   $17.4807   $17.48   $17.50   $17.50  
  Purchase #7 $116.99   11.161%   $130.0473   $130.05   $130.05   $130.00  
  7 purchase totals = $741.54       $808.4779   $808.49   $808.50   $808.50