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	$17.59	5.251%	$18.5137	$18.51	$18.50	$18.50
Purchase #2	$91.49	8.688%	$99.4387	$99.44	$99.45	$99.40
Purchase #3	$142.40	6.306%	$151.3797	$151.38	$151.40	$151.40
Purchase #4	$185.73	9.352%	$203.0995	$203.10	$203.10	$203.10
Purchase #5	$99.25	3.236%	$102.4617	$102.46	$102.45	$102.50
Purchase #6	$216.59	11.807%	$242.1628	$242.16	$242.15	$242.20
Purchase #7	$166.92	10.176%	$183.9058	$183.91	$183.90	$183.90
7 purchase totals =	$919.97		$1,000.9619	$1,000.96	$1,000.95	$1,001.00