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	$65.45	7.142%	$70.1244	$70.12	$70.10	$70.10
Purchase #2	$169.29	3.692%	$175.5402	$175.54	$175.55	$175.50
Purchase #3	$34.33	10.332%	$37.877	$37.88	$37.90	$37.90
Purchase #4	$248.99	12.399%	$279.8623	$279.86	$279.85	$279.90
Purchase #5	$167.66	12.820%	$189.154	$189.15	$189.15	$189.20
Purchase #6	$80.51	8.192%	$87.1054	$87.11	$87.10	$87.10
Purchase #7	$6.92	12.863%	$7.8101	$7.81	$7.80	$7.80
7 purchase totals =	$773.15		$847.4734	$847.47	$847.45	$847.50