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	$123.72	4.183%	$128.8952	$128.90	$128.90	$128.90
Purchase #2	$236.34	8.639%	$256.7574	$256.76	$256.75	$256.80
Purchase #3	$237.58	4.856%	$249.1169	$249.12	$249.10	$249.10
Purchase #4	$30.39	7.644%	$32.713	$32.71	$32.70	$32.70
Purchase #5	$136.80	7.143%	$146.5716	$146.57	$146.55	$146.60
Purchase #6	$129.78	9.294%	$141.8418	$141.84	$141.85	$141.80
Purchase #7	$106.92	4.578%	$111.8148	$111.81	$111.80	$111.80
7 purchase totals =	$1,001.53		$1,067.7107	$1,067.71	$1,067.65	$1,067.70