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	$44.81	12.118%	$50.2401	$50.24	$50.25	$50.20
Purchase #2	$117.87	12.135%	$132.1735	$132.17	$132.15	$132.20
Purchase #3	$223.68	5.641%	$236.2978	$236.30	$236.30	$236.30
Purchase #4	$69.54	12.391%	$78.1567	$78.16	$78.15	$78.20
Purchase #5	$128.55	13.653%	$146.1009	$146.10	$146.10	$146.10
Purchase #6	$120.43	5.731%	$127.3318	$127.33	$127.35	$127.30
Purchase #7	$58.81	12.736%	$66.3	$66.30	$66.30	$66.30
7 purchase totals =	$763.69		$836.6008	$836.60	$836.60	$836.60