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	$165.48	8.293%	$179.2033	$179.20	$179.20	$179.20
Purchase #2	$55.61	7.782%	$59.9376	$59.94	$59.95	$59.90
Purchase #3	$9.42	5.204%	$9.9102	$9.91	$9.90	$9.90
Purchase #4	$195.70	8.173%	$211.6946	$211.69	$211.70	$211.70
Purchase #5	$103.70	8.341%	$112.3496	$112.35	$112.35	$112.30
Purchase #6	$175.72	4.863%	$184.2653	$184.27	$184.25	$184.30
Purchase #7	$78.56	4.585%	$82.162	$82.16	$82.15	$82.20
7 purchase totals =	$784.19		$839.5226	$839.52	$839.50	$839.50