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	$30.51	10.590%	$33.741	$33.74	$33.75	$33.70
Purchase #2	$157.71	9.358%	$172.4685	$172.47	$172.45	$172.50
Purchase #3	$71.89	10.349%	$79.3299	$79.33	$79.35	$79.30
Purchase #4	$42.71	4.430%	$44.6021	$44.60	$44.60	$44.60
Purchase #5	$45.50	4.316%	$47.4638	$47.46	$47.45	$47.50
Purchase #6	$213.40	11.585%	$238.1224	$238.12	$238.10	$238.10
Purchase #7	$100.47	8.633%	$109.1436	$109.14	$109.15	$109.10
7 purchase totals =	$662.19		$724.8713	$724.86	$724.85	$724.80