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	$143.43	11.213%	$159.5128	$159.51	$159.50	$159.50
Purchase #2	$167.31	12.343%	$187.9611	$187.96	$187.95	$188.00
Purchase #3	$77.89	3.871%	$80.9051	$80.91	$80.90	$80.90
Purchase #4	$96.27	10.835%	$106.7009	$106.70	$106.70	$106.70
Purchase #5	$116.73	5.864%	$123.575	$123.58	$123.60	$123.60
Purchase #6	$89.81	13.385%	$101.8311	$101.83	$101.85	$101.80
Purchase #7	$22.32	6.623%	$23.7983	$23.80	$23.80	$23.80
7 purchase totals =	$713.76		$784.2843	$784.29	$784.30	$784.30