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	$129.82	8.319%	$140.6197	$140.62	$140.60	$140.60
Purchase #2	$242.29	9.749%	$265.9109	$265.91	$265.90	$265.90
Purchase #3	$205.45	11.538%	$229.1548	$229.15	$229.15	$229.20
Purchase #4	$56.34	6.285%	$59.881	$59.88	$59.90	$59.90
Purchase #5	$54.40	7.254%	$58.3462	$58.35	$58.35	$58.30
Purchase #6	$82.86	12.388%	$93.1247	$93.12	$93.10	$93.10
Purchase #7	$141.91	13.191%	$160.6293	$160.63	$160.65	$160.60
7 purchase totals =	$913.07		$1,007.6666	$1,007.66	$1,007.65	$1,007.60