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	$81.46	13.172%	$92.1899	$92.19	$92.20	$92.20
Purchase #2	$105.85	4.220%	$110.3169	$110.32	$110.30	$110.30
Purchase #3	$117.47	4.783%	$123.0886	$123.09	$123.10	$123.10
Purchase #4	$124.30	13.521%	$141.1066	$141.11	$141.10	$141.10
Purchase #5	$85.66	7.599%	$92.1693	$92.17	$92.15	$92.20
Purchase #6	$48.57	6.618%	$51.7844	$51.78	$51.80	$51.80
Purchase #7	$33.41	12.569%	$37.6093	$37.61	$37.60	$37.60
7 purchase totals =	$596.72		$648.2650	$648.27	$648.25	$648.30