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	$249.45	6.639%	$266.011	$266.01	$266.00	$266.00
Purchase #2	$65.39	10.853%	$72.4868	$72.49	$72.50	$72.50
Purchase #3	$162.99	3.279%	$168.3344	$168.33	$168.35	$168.30
Purchase #4	$64.34	11.565%	$71.7809	$71.78	$71.80	$71.80
Purchase #5	$93.40	12.536%	$105.1086	$105.11	$105.10	$105.10
Purchase #6	$160.91	9.322%	$175.91	$175.91	$175.90	$175.90
Purchase #7	$109.38	13.509%	$124.1561	$124.16	$124.15	$124.20
7 purchase totals =	$905.86		$983.7878	$983.79	$983.80	$983.80