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	$130.72	7.730%	$140.8247	$140.82	$140.80	$140.80
Purchase #2	$221.79	12.315%	$249.1034	$249.10	$249.10	$249.10
Purchase #3	$34.33	9.224%	$37.4966	$37.50	$37.50	$37.50
Purchase #4	$37.55	7.540%	$40.3813	$40.38	$40.40	$40.40
Purchase #5	$109.53	4.653%	$114.6264	$114.63	$114.65	$114.60
Purchase #6	$44.41	10.301%	$48.9847	$48.98	$49.00	$49.00
Purchase #7	$81.48	10.514%	$90.0468	$90.05	$90.05	$90.00
7 purchase totals =	$659.81		$721.4639	$721.46	$721.50	$721.40