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	$65.59	6.151%	$69.6244	$69.62	$69.60	$69.60
Purchase #2	$26.56	7.241%	$28.4832	$28.48	$28.50	$28.50
Purchase #3	$141.91	12.766%	$160.0262	$160.03	$160.05	$160.00
Purchase #4	$172.44	11.232%	$191.8085	$191.81	$191.80	$191.80
Purchase #5	$127.57	11.345%	$142.0428	$142.04	$142.05	$142.00
Purchase #6	$143.63	10.354%	$158.5015	$158.50	$158.50	$158.50
Purchase #7	$55.53	3.130%	$57.2681	$57.27	$57.25	$57.30
7 purchase totals =	$733.23		$807.7547	$807.75	$807.75	$807.70