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	$241.72	11.659%	$269.9021	$269.90	$269.90	$269.90
Purchase #2	$66.63	9.275%	$72.8099	$72.81	$72.80	$72.80
Purchase #3	$97.98	3.486%	$101.3956	$101.40	$101.40	$101.40
Purchase #4	$33.79	6.239%	$35.8982	$35.90	$35.90	$35.90
Purchase #5	$237.47	13.771%	$270.172	$270.17	$270.15	$270.20
Purchase #6	$83.56	7.391%	$89.7359	$89.74	$89.75	$89.70
Purchase #7	$54.48	11.171%	$60.566	$60.57	$60.55	$60.60
7 purchase totals =	$815.63		$900.4797	$900.49	$900.45	$900.50