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	$83.77	7.326%	$89.907	$89.91	$89.90	$89.90
Purchase #2	$189.32	13.284%	$214.4693	$214.47	$214.45	$214.50
Purchase #3	$148.56	13.535%	$168.6676	$168.67	$168.65	$168.70
Purchase #4	$31.66	12.196%	$35.5213	$35.52	$35.50	$35.50
Purchase #5	$33.36	5.625%	$35.2365	$35.24	$35.25	$35.20
Purchase #6	$165.76	5.816%	$175.4006	$175.40	$175.40	$175.40
Purchase #7	$52.39	5.674%	$55.3626	$55.36	$55.35	$55.40
7 purchase totals =	$704.82		$774.5649	$774.57	$774.50	$774.60