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	$90.26	10.547%	$99.7797	$99.78	$99.80	$99.80
Purchase #2	$16.96	9.829%	$18.627	$18.63	$18.65	$18.60
Purchase #3	$164.50	6.503%	$175.1974	$175.20	$175.20	$175.20
Purchase #4	$37.26	12.595%	$41.9529	$41.95	$41.95	$42.00
Purchase #5	$126.49	7.612%	$136.1184	$136.12	$136.10	$136.10
Purchase #6	$6.96	8.631%	$7.5607	$7.56	$7.55	$7.60
Purchase #7	$77.28	10.712%	$85.5582	$85.56	$85.55	$85.60
7 purchase totals =	$519.71		$564.7943	$564.80	$564.80	$564.90