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	$38.70	8.498%	$41.9887	$41.99	$42.00	$42.00
Purchase #2	$36.51	3.546%	$37.8046	$37.80	$37.80	$37.80
Purchase #3	$78.26	11.556%	$87.3037	$87.30	$87.30	$87.30
Purchase #4	$48.66	10.689%	$53.8613	$53.86	$53.85	$53.90
Purchase #5	$134.53	7.442%	$144.5417	$144.54	$144.55	$144.50
Purchase #6	$115.28	13.158%	$130.4485	$130.45	$130.45	$130.40
Purchase #7	$82.64	9.284%	$90.3123	$90.31	$90.30	$90.30
7 purchase totals =	$534.58		$586.2608	$586.25	$586.25	$586.20