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	$244.96	12.316%	$275.1293	$275.13	$275.15	$275.10
Purchase #2	$33.41	6.283%	$35.5092	$35.51	$35.50	$35.50
Purchase #3	$109.74	12.642%	$123.6133	$123.61	$123.60	$123.60
Purchase #4	$214.54	7.851%	$231.3835	$231.38	$231.40	$231.40
Purchase #5	$209.87	6.687%	$223.904	$223.90	$223.90	$223.90
Purchase #6	$248.58	6.731%	$265.3119	$265.31	$265.30	$265.30
Purchase #7	$243.99	8.532%	$264.8072	$264.81	$264.80	$264.80
7 purchase totals =	$1,305.09		$1,419.6584	$1,419.65	$1,419.65	$1,419.60