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	$40.90	6.825%	$43.6914	$43.69	$43.70	$43.70
Purchase #2	$221.33	3.567%	$229.2248	$229.22	$229.20	$229.20
Purchase #3	$99.35	11.246%	$110.5229	$110.52	$110.50	$110.50
Purchase #4	$93.29	9.188%	$101.8615	$101.86	$101.85	$101.90
Purchase #5	$62.70	10.407%	$69.2252	$69.23	$69.25	$69.20
Purchase #6	$61.81	13.673%	$70.2613	$70.26	$70.25	$70.30
Purchase #7	$52.51	13.774%	$59.7427	$59.74	$59.75	$59.70
7 purchase totals =	$631.89		$684.5298	$684.52	$684.50	$684.50