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	$39.56	6.624%	$42.1805	$42.18	$42.20	$42.20
Purchase #2	$95.83	3.383%	$99.0719	$99.07	$99.05	$99.10
Purchase #3	$243.29	9.234%	$265.7554	$265.76	$265.75	$265.80
Purchase #4	$216.62	10.272%	$238.8712	$238.87	$238.85	$238.90
Purchase #5	$53.42	3.277%	$55.1706	$55.17	$55.15	$55.20
Purchase #6	$24.98	9.865%	$27.4443	$27.44	$27.45	$27.40
Purchase #7	$43.70	3.596%	$45.2715	$45.27	$45.25	$45.30
7 purchase totals =	$717.40		$773.7654	$773.76	$773.70	$773.90