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	$81.31	10.149%	$89.5622	$89.56	$89.55	$89.60
Purchase #2	$151.97	13.360%	$172.2732	$172.27	$172.25	$172.30
Purchase #3	$39.30	3.764%	$40.7793	$40.78	$40.80	$40.80
Purchase #4	$29.95	10.681%	$33.149	$33.15	$33.15	$33.10
Purchase #5	$147.79	3.399%	$152.8134	$152.81	$152.80	$152.80
Purchase #6	$15.54	8.568%	$16.8715	$16.87	$16.85	$16.90
Purchase #7	$79.70	13.764%	$90.6699	$90.67	$90.65	$90.70
7 purchase totals =	$545.56		$596.1185	$596.11	$596.05	$596.20