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	$249.49	12.835%	$281.512	$281.51	$281.50	$281.50
Purchase #2	$108.91	13.333%	$123.431	$123.43	$123.45	$123.40
Purchase #3	$150.84	10.630%	$166.8743	$166.87	$166.85	$166.90
Purchase #4	$221.61	7.638%	$238.5366	$238.54	$238.55	$238.50
Purchase #5	$236.47	7.150%	$253.3776	$253.38	$253.40	$253.40
Purchase #6	$9.26	9.679%	$10.1563	$10.16	$10.15	$10.20
Purchase #7	$90.61	10.736%	$100.3379	$100.34	$100.35	$100.30
7 purchase totals =	$1,067.19		$1,174.2257	$1,174.23	$1,174.25	$1,174.20