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	$18.32	13.622%	$20.8156	$20.82	$20.80	$20.80
Purchase #2	$192.38	6.179%	$204.2672	$204.27	$204.25	$204.30
Purchase #3	$28.98	12.192%	$32.5132	$32.51	$32.50	$32.50
Purchase #4	$53.43	7.773%	$57.5831	$57.58	$57.60	$57.60
Purchase #5	$13.66	11.857%	$15.2797	$15.28	$15.30	$15.30
Purchase #6	$94.85	12.174%	$106.397	$106.40	$106.40	$106.40
Purchase #7	$138.47	7.306%	$148.5866	$148.59	$148.60	$148.60
7 purchase totals =	$540.09		$585.4424	$585.45	$585.45	$585.50