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	$98.36	13.250%	$111.3927	$111.39	$111.40	$111.40
Purchase #2	$87.90	6.723%	$93.8095	$93.81	$93.80	$93.80
Purchase #3	$151.94	12.534%	$170.9842	$170.98	$171.00	$171.00
Purchase #4	$153.77	8.506%	$166.8497	$166.85	$166.85	$166.80
Purchase #5	$186.87	12.250%	$209.7616	$209.76	$209.75	$209.80
Purchase #6	$202.89	10.199%	$223.5828	$223.58	$223.60	$223.60
Purchase #7	$151.25	13.679%	$171.9395	$171.94	$171.95	$171.90
7 purchase totals =	$1,032.98		$1,148.3200	$1,148.31	$1,148.35	$1,148.30