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	$37.89	11.764%	$42.3474	$42.35	$42.35	$42.30
Purchase #2	$244.36	13.150%	$276.4933	$276.49	$276.50	$276.50
Purchase #3	$141.96	8.700%	$154.3105	$154.31	$154.30	$154.30
Purchase #4	$98.81	3.286%	$102.0569	$102.06	$102.05	$102.10
Purchase #5	$12.65	7.850%	$13.643	$13.64	$13.65	$13.60
Purchase #6	$28.93	12.433%	$32.5269	$32.53	$32.55	$32.50
Purchase #7	$227.25	10.833%	$251.868	$251.87	$251.85	$251.90
7 purchase totals =	$791.85		$873.2460	$873.25	$873.25	$873.20