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	$39.60	7.237%	$42.4659	$42.47	$42.45	$42.50
Purchase #2	$195.58	9.274%	$213.7181	$213.72	$213.70	$213.70
Purchase #3	$69.50	4.620%	$72.7109	$72.71	$72.70	$72.70
Purchase #4	$249.31	5.143%	$262.132	$262.13	$262.15	$262.10
Purchase #5	$79.29	5.173%	$83.3917	$83.39	$83.40	$83.40
Purchase #6	$159.59	12.823%	$180.0542	$180.05	$180.05	$180.10
Purchase #7	$95.53	4.838%	$100.1517	$100.15	$100.15	$100.20
7 purchase totals =	$888.40		$954.6245	$954.62	$954.60	$954.70