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	$215.50	3.528%	$223.1028	$223.10	$223.10	$223.10
Purchase #2	$164.70	10.225%	$181.5406	$181.54	$181.55	$181.50
Purchase #3	$126.79	3.787%	$131.5915	$131.59	$131.60	$131.60
Purchase #4	$79.60	4.316%	$83.0355	$83.04	$83.05	$83.00
Purchase #5	$121.34	4.144%	$126.3683	$126.37	$126.35	$126.40
Purchase #6	$39.93	13.534%	$45.3341	$45.33	$45.35	$45.30
Purchase #7	$163.68	13.475%	$185.7359	$185.74	$185.75	$185.70
7 purchase totals =	$911.54		$976.7087	$976.71	$976.75	$976.60