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	$48.60	5.441%	$51.2443	$51.24	$51.25	$51.20
Purchase #2	$64.75	11.626%	$72.2778	$72.28	$72.30	$72.30
Purchase #3	$168.69	7.186%	$180.8121	$180.81	$180.80	$180.80
Purchase #4	$83.42	7.284%	$89.4963	$89.50	$89.50	$89.50
Purchase #5	$96.25	12.557%	$108.3361	$108.34	$108.35	$108.30
Purchase #6	$60.48	9.568%	$66.2667	$66.27	$66.25	$66.30
Purchase #7	$90.69	10.281%	$100.0138	$100.01	$100.00	$100.00
7 purchase totals =	$612.88		$668.4471	$668.45	$668.45	$668.40