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	$53.68	6.763%	$57.3104	$57.31	$57.30	$57.30
Purchase #2	$127.83	9.219%	$139.6146	$139.61	$139.60	$139.60
Purchase #3	$224.54	8.433%	$243.4755	$243.48	$243.50	$243.50
Purchase #4	$183.73	7.747%	$197.9636	$197.96	$197.95	$198.00
Purchase #5	$74.56	4.431%	$77.8638	$77.86	$77.85	$77.90
Purchase #6	$98.80	10.805%	$109.4753	$109.48	$109.50	$109.50
Purchase #7	$89.90	5.256%	$94.6251	$94.63	$94.65	$94.60
7 purchase totals =	$853.04		$920.3283	$920.33	$920.35	$920.40