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	$52.60	4.755%	$55.1011	$55.10	$55.10	$55.10
Purchase #2	$47.36	3.749%	$49.1355	$49.14	$49.15	$49.10
Purchase #3	$113.35	12.793%	$127.8509	$127.85	$127.85	$127.90
Purchase #4	$59.96	7.557%	$64.4912	$64.49	$64.50	$64.50
Purchase #5	$55.39	6.102%	$58.7699	$58.77	$58.75	$58.80
Purchase #6	$144.54	6.279%	$153.6157	$153.62	$153.60	$153.60
Purchase #7	$83.78	9.119%	$91.4199	$91.42	$91.40	$91.40
7 purchase totals =	$556.98		$600.3842	$600.39	$600.35	$600.40