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	$223.46	12.623%	$251.6674	$251.67	$251.65	$251.70
Purchase #2	$80.84	10.645%	$89.4454	$89.45	$89.45	$89.40
Purchase #3	$57.39	8.465%	$62.2481	$62.25	$62.25	$62.20
Purchase #4	$33.66	3.545%	$34.8532	$34.85	$34.85	$34.90
Purchase #5	$218.87	5.738%	$231.4288	$231.43	$231.45	$231.40
Purchase #6	$147.78	4.473%	$154.3902	$154.39	$154.40	$154.40
Purchase #7	$224.58	7.832%	$242.1691	$242.17	$242.15	$242.20
7 purchase totals =	$986.58		$1,066.2022	$1,066.21	$1,066.20	$1,066.20