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	$159.67	4.721%	$167.208	$167.21	$167.20	$167.20
Purchase #2	$132.30	6.709%	$141.176	$141.18	$141.20	$141.20
Purchase #3	$88.47	11.763%	$98.8767	$98.88	$98.90	$98.90
Purchase #4	$43.78	13.829%	$49.8343	$49.83	$49.85	$49.80
Purchase #5	$91.83	8.713%	$99.8311	$99.83	$99.85	$99.80
Purchase #6	$232.42	11.310%	$258.7067	$258.71	$258.70	$258.70
Purchase #7	$159.83	4.277%	$166.6659	$166.67	$166.65	$166.70
7 purchase totals =	$908.30		$982.2987	$982.31	$982.35	$982.30