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	$39.69	11.201%	$44.1357	$44.14	$44.15	$44.10
Purchase #2	$85.43	5.597%	$90.2115	$90.21	$90.20	$90.20
Purchase #3	$34.50	12.357%	$38.7632	$38.76	$38.75	$38.80
Purchase #4	$6.73	11.820%	$7.5255	$7.53	$7.55	$7.50
Purchase #5	$198.81	9.826%	$218.3451	$218.35	$218.35	$218.30
Purchase #6	$250.42	10.118%	$275.7575	$275.76	$275.75	$275.80
Purchase #7	$181.90	4.370%	$189.849	$189.85	$189.85	$189.80
7 purchase totals =	$797.48		$864.5875	$864.60	$864.60	$864.50