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	$160.81	5.731%	$170.026	$170.03	$170.05	$170.00
Purchase #2	$176.87	11.169%	$196.6246	$196.62	$196.60	$196.60
Purchase #3	$166.40	11.259%	$185.135	$185.14	$185.15	$185.10
Purchase #4	$230.98	10.473%	$255.1705	$255.17	$255.15	$255.20
Purchase #5	$43.90	6.465%	$46.7381	$46.74	$46.75	$46.70
Purchase #6	$27.35	6.674%	$29.1753	$29.18	$29.20	$29.20
Purchase #7	$106.89	12.744%	$120.5121	$120.51	$120.50	$120.50
7 purchase totals =	$913.20		$1,003.3816	$1,003.39	$1,003.40	$1,003.30