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	$9.87	4.535%	$10.3176	$10.32	$10.30	$10.30
Purchase #2	$233.56	11.806%	$261.1341	$261.13	$261.15	$261.10
Purchase #3	$247.89	8.874%	$269.8878	$269.89	$269.90	$269.90
Purchase #4	$141.54	8.646%	$153.7775	$153.78	$153.80	$153.80
Purchase #5	$152.61	9.540%	$167.169	$167.17	$167.15	$167.20
Purchase #6	$203.48	3.242%	$210.0768	$210.08	$210.10	$210.10
Purchase #7	$89.73	11.263%	$99.8363	$99.84	$99.85	$99.80
7 purchase totals =	$1,078.68		$1,172.1991	$1,172.21	$1,172.25	$1,172.20