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	$90.53	9.392%	$99.0326	$99.03	$99.05	$99.00
Purchase #2	$115.85	11.751%	$129.4635	$129.46	$129.45	$129.50
Purchase #3	$158.81	8.345%	$172.0627	$172.06	$172.05	$172.10
Purchase #4	$145.89	11.428%	$162.5623	$162.56	$162.55	$162.60
Purchase #5	$160.44	5.376%	$169.0653	$169.07	$169.05	$169.10
Purchase #6	$28.29	4.413%	$29.5384	$29.54	$29.55	$29.50
Purchase #7	$239.40	10.700%	$265.0158	$265.02	$265.00	$265.00
7 purchase totals =	$939.21		$1,026.7406	$1,026.74	$1,026.70	$1,026.80