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	$42.91	13.151%	$48.5531	$48.55	$48.55	$48.60
Purchase #2	$66.64	3.762%	$69.147	$69.15	$69.15	$69.10
Purchase #3	$136.37	11.466%	$152.0062	$152.01	$152.00	$152.00
Purchase #4	$88.96	13.146%	$100.6547	$100.65	$100.65	$100.70
Purchase #5	$82.25	3.629%	$85.2349	$85.23	$85.25	$85.20
Purchase #6	$98.33	4.514%	$102.7686	$102.77	$102.75	$102.80
Purchase #7	$23.47	3.764%	$24.3534	$24.35	$24.35	$24.40
7 purchase totals =	$538.93		$582.7179	$582.71	$582.70	$582.80