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	$32.49	8.580%	$35.2776	$35.28	$35.30	$35.30
Purchase #2	$34.88	10.539%	$38.556	$38.56	$38.55	$38.60
Purchase #3	$232.83	8.790%	$253.2958	$253.30	$253.30	$253.30
Purchase #4	$124.51	13.695%	$141.5616	$141.56	$141.55	$141.60
Purchase #5	$22.44	11.468%	$25.0134	$25.01	$25.00	$25.00
Purchase #6	$130.38	6.326%	$138.6278	$138.63	$138.65	$138.60
Purchase #7	$88.33	12.390%	$99.2741	$99.27	$99.25	$99.30
7 purchase totals =	$665.86		$731.6063	$731.61	$731.60	$731.70