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	$48.62	7.850%	$52.4367	$52.44	$52.45	$52.40
Purchase #2	$175.72	11.652%	$196.1949	$196.19	$196.20	$196.20
Purchase #3	$37.55	7.414%	$40.334	$40.33	$40.35	$40.30
Purchase #4	$73.98	11.654%	$82.6016	$82.60	$82.60	$82.60
Purchase #5	$46.45	6.413%	$49.4288	$49.43	$49.45	$49.40
Purchase #6	$46.39	6.510%	$49.41	$49.41	$49.40	$49.40
Purchase #7	$154.70	11.282%	$172.1533	$172.15	$172.15	$172.20
7 purchase totals =	$583.41		$642.5593	$642.55	$642.60	$642.50