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	$28.75	12.384%	$32.3104	$32.31	$32.30	$32.30
Purchase #2	$152.41	5.709%	$161.1111	$161.11	$161.10	$161.10
Purchase #3	$137.73	7.848%	$148.5391	$148.54	$148.55	$148.50
Purchase #4	$73.71	12.675%	$83.0527	$83.05	$83.05	$83.10
Purchase #5	$34.67	3.461%	$35.8699	$35.87	$35.85	$35.90
Purchase #6	$151.75	6.276%	$161.2738	$161.27	$161.25	$161.30
Purchase #7	$52.44	6.256%	$55.7206	$55.72	$55.70	$55.70
7 purchase totals =	$631.46		$677.8776	$677.87	$677.80	$677.90