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	$94.57	5.840%	$100.0929	$100.09	$100.10	$100.10
Purchase #2	$176.77	5.456%	$186.4146	$186.41	$186.40	$186.40
Purchase #3	$142.95	6.722%	$152.5591	$152.56	$152.55	$152.60
Purchase #4	$38.91	3.815%	$40.3944	$40.39	$40.40	$40.40
Purchase #5	$11.96	6.601%	$12.7495	$12.75	$12.75	$12.70
Purchase #6	$233.98	8.644%	$254.2052	$254.21	$254.20	$254.20
Purchase #7	$44.52	11.470%	$49.6264	$49.63	$49.65	$49.60
7 purchase totals =	$743.66		$796.0421	$796.04	$796.05	$796.00