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	$112.81	7.639%	$121.4276	$121.43	$121.45	$121.40
Purchase #2	$143.30	11.307%	$159.5029	$159.50	$159.50	$159.50
Purchase #3	$92.75	11.468%	$103.3866	$103.39	$103.40	$103.40
Purchase #4	$148.73	9.332%	$162.6095	$162.61	$162.60	$162.60
Purchase #5	$67.52	8.569%	$73.3058	$73.31	$73.30	$73.30
Purchase #6	$28.52	7.323%	$30.6085	$30.61	$30.60	$30.60
Purchase #7	$89.47	11.210%	$99.4996	$99.50	$99.50	$99.50
7 purchase totals =	$683.10		$750.3405	$750.35	$750.35	$750.30