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	$116.90	6.835%	$124.8901	$124.89	$124.90	$124.90
Purchase #2	$85.72	3.618%	$88.8213	$88.82	$88.80	$88.80
Purchase #3	$50.51	6.378%	$53.7315	$53.73	$53.75	$53.70
Purchase #4	$51.94	10.238%	$57.2576	$57.26	$57.25	$57.30
Purchase #5	$92.65	13.579%	$105.2309	$105.23	$105.25	$105.20
Purchase #6	$63.28	11.402%	$70.4952	$70.50	$70.50	$70.50
Purchase #7	$127.84	5.650%	$135.063	$135.06	$135.05	$135.10
7 purchase totals =	$588.84		$635.4896	$635.49	$635.50	$635.50