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	$100.57	12.366%	$113.0065	$113.01	$113.00	$113.00
Purchase #2	$234.51	12.601%	$264.0606	$264.06	$264.05	$264.10
Purchase #3	$137.73	9.735%	$151.138	$151.14	$151.15	$151.10
Purchase #4	$111.83	8.244%	$121.0493	$121.05	$121.05	$121.00
Purchase #5	$233.89	3.435%	$241.9241	$241.92	$241.90	$241.90
Purchase #6	$82.84	10.709%	$91.7113	$91.71	$91.70	$91.70
Purchase #7	$158.67	6.758%	$169.3929	$169.39	$169.40	$169.40
7 purchase totals =	$1,060.04		$1,152.2827	$1,152.28	$1,152.25	$1,152.20