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	$83.62	8.691%	$90.8874	$90.89	$90.90	$90.90
Purchase #2	$35.74	3.496%	$36.9895	$36.99	$37.00	$37.00
Purchase #3	$54.71	9.207%	$59.7471	$59.75	$59.75	$59.70
Purchase #4	$35.76	5.472%	$37.7168	$37.72	$37.70	$37.70
Purchase #5	$106.29	6.759%	$113.4741	$113.47	$113.45	$113.50
Purchase #6	$212.85	7.244%	$228.2689	$228.27	$228.25	$228.30
Purchase #7	$197.86	9.219%	$216.1007	$216.10	$216.10	$216.10
7 purchase totals =	$726.83		$783.1845	$783.19	$783.15	$783.20