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	$154.50	11.843%	$172.7974	$172.80	$172.80	$172.80
Purchase #2	$37.82	3.562%	$39.1671	$39.17	$39.15	$39.20
Purchase #3	$79.95	12.272%	$89.7615	$89.76	$89.75	$89.80
Purchase #4	$172.42	6.593%	$183.7877	$183.79	$183.80	$183.80
Purchase #5	$211.47	8.426%	$229.2885	$229.29	$229.30	$229.30
Purchase #6	$40.39	6.536%	$43.0299	$43.03	$43.05	$43.00
Purchase #7	$28.89	8.241%	$31.2708	$31.27	$31.25	$31.30
7 purchase totals =	$725.44		$789.1029	$789.11	$789.10	$789.20