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	$128.78	8.117%	$139.2331	$139.23	$139.25	$139.20
Purchase #2	$205.47	13.549%	$233.3091	$233.31	$233.30	$233.30
Purchase #3	$54.79	13.764%	$62.3313	$62.33	$62.35	$62.30
Purchase #4	$146.75	12.670%	$165.3432	$165.34	$165.35	$165.30
Purchase #5	$123.53	8.438%	$133.9535	$133.95	$133.95	$134.00
Purchase #6	$112.38	10.760%	$124.4721	$124.47	$124.45	$124.50
Purchase #7	$144.73	10.280%	$159.6082	$159.61	$159.60	$159.60
7 purchase totals =	$916.43		$1,018.2505	$1,018.24	$1,018.25	$1,018.20