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	$30.34	6.567%	$32.3324	$32.33	$32.35	$32.30
Purchase #2	$230.91	11.195%	$256.7604	$256.76	$256.75	$256.80
Purchase #3	$146.78	3.110%	$151.3449	$151.34	$151.35	$151.30
Purchase #4	$200.53	8.836%	$218.2488	$218.25	$218.25	$218.20
Purchase #5	$207.37	5.701%	$219.1922	$219.19	$219.20	$219.20
Purchase #6	$70.35	11.348%	$78.3333	$78.33	$78.35	$78.30
Purchase #7	$138.33	12.793%	$156.0266	$156.03	$156.05	$156.00
7 purchase totals =	$1,024.61		$1,112.2386	$1,112.23	$1,112.30	$1,112.10