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	$35.42	9.858%	$38.9117	$38.91	$38.90	$38.90
Purchase #2	$161.91	11.569%	$180.6414	$180.64	$180.65	$180.60
Purchase #3	$28.42	7.178%	$30.46	$30.46	$30.45	$30.50
Purchase #4	$93.67	12.591%	$105.464	$105.46	$105.45	$105.50
Purchase #5	$199.88	11.274%	$222.4145	$222.41	$222.40	$222.40
Purchase #6	$134.37	3.613%	$139.2248	$139.22	$139.20	$139.20
Purchase #7	$81.84	8.114%	$88.4805	$88.48	$88.50	$88.50
7 purchase totals =	$735.51		$805.5969	$805.58	$805.55	$805.60