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	$37.33	10.269%	$41.1634	$41.16	$41.15	$41.20
Purchase #2	$59.60	9.770%	$65.4229	$65.42	$65.40	$65.40
Purchase #3	$208.81	7.150%	$223.7399	$223.74	$223.75	$223.70
Purchase #4	$18.25	9.502%	$19.9841	$19.98	$20.00	$20.00
Purchase #5	$10.81	13.158%	$12.2324	$12.23	$12.25	$12.20
Purchase #6	$101.89	4.323%	$106.2947	$106.29	$106.30	$106.30
Purchase #7	$189.41	5.138%	$199.1419	$199.14	$199.15	$199.10
7 purchase totals =	$626.10		$667.9793	$667.96	$668.00	$667.90