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	$235.81	3.700%	$244.535	$244.54	$244.55	$244.50
Purchase #2	$108.47	9.860%	$119.1651	$119.17	$119.15	$119.20
Purchase #3	$163.69	13.341%	$185.5279	$185.53	$185.55	$185.50
Purchase #4	$161.51	10.525%	$178.5089	$178.51	$178.50	$178.50
Purchase #5	$6.65	10.159%	$7.3256	$7.33	$7.35	$7.30
Purchase #6	$6.75	12.549%	$7.5971	$7.60	$7.60	$7.60
Purchase #7	$48.90	4.867%	$51.28	$51.28	$51.30	$51.30
7 purchase totals =	$731.78		$793.9396	$793.96	$794.00	$793.90