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	$103.62	3.362%	$107.1037	$107.10	$107.10	$107.10
Purchase #2	$63.40	11.793%	$70.8768	$70.88	$70.90	$70.90
Purchase #3	$42.90	12.182%	$48.1261	$48.13	$48.15	$48.10
Purchase #4	$56.81	6.394%	$60.4424	$60.44	$60.45	$60.40
Purchase #5	$185.66	5.588%	$196.0347	$196.03	$196.05	$196.00
Purchase #6	$83.89	7.181%	$89.9141	$89.91	$89.90	$89.90
Purchase #7	$131.42	6.275%	$139.6666	$139.67	$139.65	$139.70
7 purchase totals =	$667.70		$712.1644	$712.16	$712.20	$712.10