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	$150.91	13.184%	$170.806	$170.81	$170.80	$170.80
Purchase #2	$207.29	4.298%	$216.1993	$216.20	$216.20	$216.20
Purchase #3	$111.26	7.726%	$119.8559	$119.86	$119.85	$119.90
Purchase #4	$120.50	6.163%	$127.9264	$127.93	$127.95	$127.90
Purchase #5	$94.27	12.222%	$105.7917	$105.79	$105.80	$105.80
Purchase #6	$150.82	6.391%	$160.4589	$160.46	$160.45	$160.50
Purchase #7	$128.47	7.586%	$138.2157	$138.22	$138.20	$138.20
7 purchase totals =	$963.52		$1,039.2539	$1,039.27	$1,039.25	$1,039.30