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	$54.35	7.484%	$58.4176	$58.42	$58.40	$58.40
Purchase #2	$149.31	12.771%	$168.3784	$168.38	$168.40	$168.40
Purchase #3	$189.54	13.813%	$215.7212	$215.72	$215.70	$215.70
Purchase #4	$17.86	12.266%	$20.0507	$20.05	$20.05	$20.10
Purchase #5	$49.29	9.189%	$53.8193	$53.82	$53.80	$53.80
Purchase #6	$104.73	3.466%	$108.3599	$108.36	$108.35	$108.40
Purchase #7	$61.82	9.776%	$67.8635	$67.86	$67.85	$67.90
7 purchase totals =	$626.90		$692.6106	$692.61	$692.55	$692.70