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	$164.48	12.659%	$185.3015	$185.30	$185.30	$185.30
Purchase #2	$50.31	10.513%	$55.5991	$55.60	$55.60	$55.60
Purchase #3	$178.82	4.140%	$186.2231	$186.22	$186.20	$186.20
Purchase #4	$176.86	7.128%	$189.4666	$189.47	$189.45	$189.50
Purchase #5	$99.73	10.749%	$110.45	$110.45	$110.45	$110.50
Purchase #6	$203.87	10.386%	$225.0439	$225.04	$225.05	$225.00
Purchase #7	$36.33	6.196%	$38.581	$38.58	$38.60	$38.60
7 purchase totals =	$910.40		$990.6652	$990.66	$990.65	$990.70