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 $208.49   5.166%   $219.2606   $219.26   $219.25   $219.30  
  Purchase #2 $30.76   12.258%   $34.5306   $34.53   $34.55   $34.50  
  Purchase #3 $5.89   8.663%   $6.4003   $6.40   $6.40   $6.40  
  Purchase #4 $165.31   7.297%   $177.3727   $177.37   $177.35   $177.40  
  Purchase #5 $159.53   11.166%   $177.3431   $177.34   $177.35   $177.30  
  Purchase #6 $192.59   13.380%   $218.3585   $218.36   $218.35   $218.40  
  Purchase #7 $122.51   9.190%   $133.7687   $133.77   $133.75   $133.80  
  7 purchase totals = $885.08       $967.0345   $967.03   $967.00   $967.10