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	$50.79	12.537%	$57.1575	$57.16	$57.15	$57.20
Purchase #2	$115.91	10.289%	$127.836	$127.84	$127.85	$127.80
Purchase #3	$81.82	12.472%	$92.0246	$92.02	$92.00	$92.00
Purchase #4	$57.92	5.798%	$61.2782	$61.28	$61.30	$61.30
Purchase #5	$146.77	7.196%	$157.3316	$157.33	$157.35	$157.30
Purchase #6	$25.82	8.620%	$28.0457	$28.05	$28.05	$28.00
Purchase #7	$208.53	6.635%	$222.366	$222.37	$222.35	$222.40
7 purchase totals =	$687.56		$746.0396	$746.05	$746.05	$746.00