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	$90.77	10.480%	$100.2827	$100.28	$100.30	$100.30
Purchase #2	$99.40	11.557%	$110.8877	$110.89	$110.90	$110.90
Purchase #3	$216.64	8.809%	$235.7238	$235.72	$235.70	$235.70
Purchase #4	$14.55	7.469%	$15.6367	$15.64	$15.65	$15.60
Purchase #5	$51.36	5.812%	$54.345	$54.35	$54.35	$54.30
Purchase #6	$114.59	10.218%	$126.2988	$126.30	$126.30	$126.30
Purchase #7	$102.72	10.153%	$113.1492	$113.15	$113.15	$113.10
7 purchase totals =	$690.03		$756.3239	$756.33	$756.35	$756.20