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	$222.34	7.367%	$238.7198	$238.72	$238.70	$238.70
Purchase #2	$229.73	6.143%	$243.8423	$243.84	$243.85	$243.80
Purchase #3	$83.64	10.503%	$92.4247	$92.42	$92.40	$92.40
Purchase #4	$112.49	12.690%	$126.765	$126.77	$126.75	$126.80
Purchase #5	$120.49	3.589%	$124.8144	$124.81	$124.80	$124.80
Purchase #6	$203.87	12.861%	$230.0897	$230.09	$230.10	$230.10
Purchase #7	$37.82	12.482%	$42.5407	$42.54	$42.55	$42.50
7 purchase totals =	$1,010.38		$1,099.1966	$1,099.19	$1,099.15	$1,099.10