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	$35.62	3.656%	$36.9223	$36.92	$36.90	$36.90
Purchase #2	$215.58	8.510%	$233.9259	$233.93	$233.95	$233.90
Purchase #3	$241.39	5.313%	$254.2151	$254.22	$254.20	$254.20
Purchase #4	$191.28	6.512%	$203.7362	$203.74	$203.75	$203.70
Purchase #5	$65.50	9.108%	$71.4657	$71.47	$71.45	$71.50
Purchase #6	$63.98	11.789%	$71.5226	$71.52	$71.50	$71.50
Purchase #7	$45.57	5.680%	$48.1584	$48.16	$48.15	$48.20
7 purchase totals =	$858.92		$919.9462	$919.96	$919.90	$919.90