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	$76.26	9.642%	$83.613	$83.61	$83.60	$83.60
Purchase #2	$110.52	13.416%	$125.3474	$125.35	$125.35	$125.30
Purchase #3	$57.96	6.793%	$61.8972	$61.90	$61.90	$61.90
Purchase #4	$114.98	4.746%	$120.437	$120.44	$120.45	$120.40
Purchase #5	$45.89	8.721%	$49.8921	$49.89	$49.90	$49.90
Purchase #6	$50.29	10.630%	$55.6358	$55.64	$55.65	$55.60
Purchase #7	$152.56	11.612%	$170.2753	$170.28	$170.30	$170.30
7 purchase totals =	$608.46		$667.0978	$667.11	$667.15	$667.00