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	$37.59	13.416%	$42.6331	$42.63	$42.65	$42.60
Purchase #2	$199.41	12.191%	$223.7201	$223.72	$223.70	$223.70
Purchase #3	$81.29	3.179%	$83.8742	$83.87	$83.85	$83.90
Purchase #4	$60.83	8.512%	$66.0078	$66.01	$66.00	$66.00
Purchase #5	$14.81	6.391%	$15.7565	$15.76	$15.75	$15.80
Purchase #6	$55.74	11.623%	$62.2187	$62.22	$62.20	$62.20
Purchase #7	$244.37	12.675%	$275.3439	$275.34	$275.35	$275.30
7 purchase totals =	$694.04		$769.5543	$769.55	$769.50	$769.50