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 $9.27   6.717%   $9.8927   $9.89   $9.90   $9.90  
  Purchase #2 $177.50   3.839%   $184.3142   $184.31   $184.30   $184.30  
  Purchase #3 $64.56   10.715%   $71.4776   $71.48   $71.50   $71.50  
  Purchase #4 $95.39   8.843%   $103.8253   $103.83   $103.85   $103.80  
  Purchase #5 $99.43   10.622%   $109.9915   $109.99   $110.00   $110.00  
  Purchase #6 $119.35   9.532%   $130.7264   $130.73   $130.75   $130.70  
  Purchase #7 $49.50   4.129%   $51.5439   $51.54   $51.55   $51.50  
  7 purchase totals = $615.00       $661.7716   $661.77   $661.85   $661.70