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	$152.42	10.596%	$168.5704	$168.57	$168.55	$168.60
Purchase #2	$53.28	10.848%	$59.0598	$59.06	$59.05	$59.10
Purchase #3	$103.85	11.233%	$115.5155	$115.52	$115.50	$115.50
Purchase #4	$244.84	10.610%	$270.8175	$270.82	$270.80	$270.80
Purchase #5	$87.36	3.825%	$90.7015	$90.70	$90.70	$90.70
Purchase #6	$104.90	5.810%	$110.9947	$110.99	$111.00	$111.00
Purchase #7	$35.82	9.607%	$39.2612	$39.26	$39.25	$39.30
7 purchase totals =	$782.47		$854.9206	$854.92	$854.85	$855.00