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	$100.71	10.669%	$111.4547	$111.45	$111.45	$111.50
Purchase #2	$140.41	7.442%	$150.8593	$150.86	$150.85	$150.90
Purchase #3	$239.63	10.382%	$264.5084	$264.51	$264.50	$264.50
Purchase #4	$137.83	8.656%	$149.7606	$149.76	$149.75	$149.80
Purchase #5	$200.46	3.622%	$207.7207	$207.72	$207.70	$207.70
Purchase #6	$170.57	12.459%	$191.8213	$191.82	$191.80	$191.80
Purchase #7	$177.66	9.456%	$194.4595	$194.46	$194.45	$194.50
7 purchase totals =	$1,167.27		$1,270.5845	$1,270.58	$1,270.50	$1,270.70