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	$210.32	6.220%	$223.4019	$223.40	$223.40	$223.40
Purchase #2	$211.52	12.261%	$237.4545	$237.45	$237.45	$237.50
Purchase #3	$167.96	3.817%	$174.371	$174.37	$174.35	$174.40
Purchase #4	$29.32	4.779%	$30.7212	$30.72	$30.70	$30.70
Purchase #5	$66.63	5.792%	$70.4892	$70.49	$70.50	$70.50
Purchase #6	$83.72	6.861%	$89.464	$89.46	$89.45	$89.50
Purchase #7	$14.39	11.206%	$16.0025	$16.00	$16.00	$16.00
7 purchase totals =	$783.86		$841.9043	$841.89	$841.85	$842.00