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	$16.88	7.215%	$18.0979	$18.10	$18.10	$18.10
Purchase #2	$85.88	8.205%	$92.9265	$92.93	$92.95	$92.90
Purchase #3	$100.27	7.764%	$108.055	$108.06	$108.05	$108.10
Purchase #4	$129.75	9.837%	$142.5135	$142.51	$142.50	$142.50
Purchase #5	$135.51	4.419%	$141.4982	$141.50	$141.50	$141.50
Purchase #6	$48.43	3.701%	$50.2224	$50.22	$50.20	$50.20
Purchase #7	$170.74	8.855%	$185.859	$185.86	$185.85	$185.90
7 purchase totals =	$687.46		$739.1725	$739.18	$739.15	$739.20