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	$238.65	5.365%	$251.4536	$251.45	$251.45	$251.50
Purchase #2	$172.65	12.865%	$194.8614	$194.86	$194.85	$194.90
Purchase #3	$37.78	3.342%	$39.0426	$39.04	$39.05	$39.00
Purchase #4	$114.80	8.571%	$124.6395	$124.64	$124.65	$124.60
Purchase #5	$108.73	7.442%	$116.8217	$116.82	$116.80	$116.80
Purchase #6	$158.39	5.524%	$167.1395	$167.14	$167.15	$167.10
Purchase #7	$101.92	7.560%	$109.6252	$109.63	$109.65	$109.60
7 purchase totals =	$932.92		$1,003.5835	$1,003.58	$1,003.60	$1,003.50