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	$5.49	11.129%	$6.101	$6.10	$6.10	$6.10
Purchase #2	$38.71	10.208%	$42.6615	$42.66	$42.65	$42.70
Purchase #3	$174.46	6.195%	$185.2678	$185.27	$185.25	$185.30
Purchase #4	$242.80	13.584%	$275.782	$275.78	$275.80	$275.80
Purchase #5	$33.27	5.752%	$35.1837	$35.18	$35.20	$35.20
Purchase #6	$39.33	13.827%	$44.7682	$44.77	$44.75	$44.80
Purchase #7	$71.80	7.794%	$77.3961	$77.40	$77.40	$77.40
7 purchase totals =	$605.86		$667.1603	$667.16	$667.15	$667.30