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	$35.84	10.807%	$39.7132	$39.71	$39.70	$39.70
Purchase #2	$223.85	9.397%	$244.8852	$244.89	$244.90	$244.90
Purchase #3	$36.70	6.377%	$39.0404	$39.04	$39.05	$39.00
Purchase #4	$237.37	3.191%	$244.9445	$244.94	$244.95	$244.90
Purchase #5	$10.38	4.570%	$10.8544	$10.85	$10.85	$10.90
Purchase #6	$135.56	10.202%	$149.3898	$149.39	$149.40	$149.40
Purchase #7	$33.60	12.396%	$37.7651	$37.77	$37.75	$37.80
7 purchase totals =	$713.30		$766.5926	$766.59	$766.60	$766.60