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	$151.51	12.701%	$170.7533	$170.75	$170.75	$170.80
Purchase #2	$243.49	9.481%	$266.5753	$266.58	$266.60	$266.60
Purchase #3	$102.28	3.459%	$105.8179	$105.82	$105.80	$105.80
Purchase #4	$212.40	7.507%	$228.3449	$228.34	$228.35	$228.30
Purchase #5	$81.96	10.768%	$90.7855	$90.79	$90.80	$90.80
Purchase #6	$104.29	7.130%	$111.7259	$111.73	$111.75	$111.70
Purchase #7	$164.36	13.707%	$186.8888	$186.89	$186.90	$186.90
7 purchase totals =	$1,060.29		$1,160.8916	$1,160.90	$1,160.95	$1,160.90