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	$147.76	12.476%	$166.1945	$166.19	$166.20	$166.20
Purchase #2	$51.79	3.265%	$53.4809	$53.48	$53.50	$53.50
Purchase #3	$220.53	8.226%	$238.6708	$238.67	$238.65	$238.70
Purchase #4	$225.63	12.770%	$254.443	$254.44	$254.45	$254.40
Purchase #5	$34.79	7.660%	$37.4549	$37.45	$37.45	$37.50
Purchase #6	$136.48	8.623%	$148.2487	$148.25	$148.25	$148.20
Purchase #7	$47.33	12.754%	$53.3665	$53.37	$53.35	$53.40
7 purchase totals =	$864.31		$951.8593	$951.85	$951.85	$951.90