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	$240.88	13.456%	$273.2928	$273.29	$273.30	$273.30
Purchase #2	$248.50	10.527%	$274.6596	$274.66	$274.65	$274.70
Purchase #3	$171.86	6.229%	$182.5652	$182.57	$182.55	$182.60
Purchase #4	$217.67	8.136%	$235.3796	$235.38	$235.40	$235.40
Purchase #5	$208.79	12.233%	$234.3313	$234.33	$234.35	$234.30
Purchase #6	$85.89	8.197%	$92.9304	$92.93	$92.95	$92.90
Purchase #7	$25.40	9.732%	$27.8719	$27.87	$27.85	$27.90
7 purchase totals =	$1,198.99		$1,321.0308	$1,321.03	$1,321.05	$1,321.10