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 $235.66   8.103%   $254.7555   $254.76   $254.75   $254.80  
  Purchase #2 $55.56   4.866%   $58.2635   $58.26   $58.25   $58.30  
  Purchase #3 $54.31   13.138%   $61.4452   $61.45   $61.45   $61.40  
  Purchase #4 $91.43   11.266%   $101.7305   $101.73   $101.75   $101.70  
  Purchase #5 $107.95   8.346%   $116.9595   $116.96   $116.95   $117.00  
  Purchase #6 $163.68   8.296%   $177.2589   $177.26   $177.25   $177.30  
  Purchase #7 $213.40   11.311%   $237.5377   $237.54   $237.55   $237.50  
  7 purchase totals = $921.99       $1,007.9508   $1,007.96   $1,007.95   $1,008.00