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	$225.40	8.414%	$244.3652	$244.37	$244.35	$244.40
Purchase #2	$99.30	10.679%	$109.9042	$109.90	$109.90	$109.90
Purchase #3	$185.61	12.843%	$209.4479	$209.45	$209.45	$209.40
Purchase #4	$247.39	3.435%	$255.8878	$255.89	$255.90	$255.90
Purchase #5	$184.31	5.532%	$194.506	$194.51	$194.50	$194.50
Purchase #6	$131.88	9.867%	$144.8926	$144.89	$144.90	$144.90
Purchase #7	$166.75	7.403%	$179.0945	$179.09	$179.10	$179.10
7 purchase totals =	$1,240.64		$1,338.0982	$1,338.10	$1,338.10	$1,338.10