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	$78.65	13.496%	$89.2646	$89.26	$89.25	$89.30
Purchase #2	$231.77	13.456%	$262.957	$262.96	$262.95	$263.00
Purchase #3	$83.40	8.120%	$90.1721	$90.17	$90.15	$90.20
Purchase #4	$183.84	3.218%	$189.756	$189.76	$189.75	$189.80
Purchase #5	$221.30	13.253%	$250.6289	$250.63	$250.65	$250.60
Purchase #6	$18.51	13.842%	$21.0722	$21.07	$21.05	$21.10
Purchase #7	$211.51	8.322%	$229.1119	$229.11	$229.10	$229.10
7 purchase totals =	$1,028.98		$1,132.9627	$1,132.96	$1,132.90	$1,133.10