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	$128.31	10.135%	$141.3142	$141.31	$141.30	$141.30
Purchase #2	$138.62	3.682%	$143.724	$143.72	$143.70	$143.70
Purchase #3	$79.33	13.532%	$90.0649	$90.06	$90.05	$90.10
Purchase #4	$47.51	6.414%	$50.5573	$50.56	$50.55	$50.60
Purchase #5	$240.33	5.763%	$254.1802	$254.18	$254.20	$254.20
Purchase #6	$110.56	11.785%	$123.5895	$123.59	$123.60	$123.60
Purchase #7	$186.26	4.292%	$194.2543	$194.25	$194.25	$194.30
7 purchase totals =	$930.92		$997.6844	$997.67	$997.65	$997.80