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	$19.29	7.345%	$20.7069	$20.71	$20.70	$20.70
Purchase #2	$120.38	13.303%	$136.3942	$136.39	$136.40	$136.40
Purchase #3	$73.80	13.739%	$83.9394	$83.94	$83.95	$83.90
Purchase #4	$243.46	10.411%	$268.8066	$268.81	$268.80	$268.80
Purchase #5	$56.70	9.161%	$61.8943	$61.89	$61.90	$61.90
Purchase #6	$48.94	9.328%	$53.5051	$53.51	$53.50	$53.50
Purchase #7	$92.92	12.185%	$104.2423	$104.24	$104.25	$104.20
7 purchase totals =	$655.49		$729.4888	$729.49	$729.50	$729.40