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	$130.49	11.358%	$145.3111	$145.31	$145.30	$145.30
Purchase #2	$210.54	12.223%	$236.2743	$236.27	$236.25	$236.30
Purchase #3	$65.78	13.779%	$74.8438	$74.84	$74.85	$74.80
Purchase #4	$120.68	6.543%	$128.5761	$128.58	$128.60	$128.60
Purchase #5	$162.35	13.676%	$184.553	$184.55	$184.55	$184.60
Purchase #6	$105.66	3.720%	$109.5906	$109.59	$109.60	$109.60
Purchase #7	$246.27	10.216%	$271.4289	$271.43	$271.45	$271.40
7 purchase totals =	$1,041.77		$1,150.5778	$1,150.57	$1,150.60	$1,150.60