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	$158.87	8.575%	$172.4931	$172.49	$172.50	$172.50
Purchase #2	$48.29	5.231%	$50.816	$50.82	$50.80	$50.80
Purchase #3	$177.59	8.166%	$192.092	$192.09	$192.10	$192.10
Purchase #4	$69.39	3.476%	$71.802	$71.80	$71.80	$71.80
Purchase #5	$178.57	7.511%	$191.9824	$191.98	$192.00	$192.00
Purchase #6	$130.31	12.812%	$147.0053	$147.01	$147.00	$147.00
Purchase #7	$98.64	13.348%	$111.8065	$111.81	$111.80	$111.80
7 purchase totals =	$861.66		$937.9973	$938.00	$938.00	$938.00