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	$172.94	5.559%	$182.5537	$182.55	$182.55	$182.60
Purchase #2	$35.39	10.490%	$39.1024	$39.10	$39.10	$39.10
Purchase #3	$223.83	8.612%	$243.1062	$243.11	$243.10	$243.10
Purchase #4	$88.57	8.201%	$95.8336	$95.83	$95.85	$95.80
Purchase #5	$28.84	12.680%	$32.4969	$32.50	$32.50	$32.50
Purchase #6	$159.31	12.714%	$179.5647	$179.56	$179.55	$179.60
Purchase #7	$88.91	9.757%	$97.5849	$97.58	$97.60	$97.60
7 purchase totals =	$797.79		$870.2424	$870.23	$870.25	$870.30