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	$58.53	12.849%	$66.0505	$66.05	$66.05	$66.10
Purchase #2	$5.78	6.469%	$6.1539	$6.15	$6.15	$6.20
Purchase #3	$120.33	8.346%	$130.3727	$130.37	$130.35	$130.40
Purchase #4	$35.80	4.245%	$37.3197	$37.32	$37.30	$37.30
Purchase #5	$123.59	3.844%	$128.3408	$128.34	$128.35	$128.30
Purchase #6	$88.90	3.676%	$92.168	$92.17	$92.15	$92.20
Purchase #7	$106.41	12.599%	$119.8166	$119.82	$119.80	$119.80
7 purchase totals =	$539.34		$580.2222	$580.22	$580.15	$580.30