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	$49.96	12.821%	$56.3654	$56.37	$56.35	$56.40
Purchase #2	$174.63	3.866%	$181.3812	$181.38	$181.40	$181.40
Purchase #3	$24.37	11.331%	$27.1314	$27.13	$27.15	$27.10
Purchase #4	$80.58	10.287%	$88.8693	$88.87	$88.85	$88.90
Purchase #5	$223.40	9.810%	$245.3155	$245.32	$245.30	$245.30
Purchase #6	$7.94	13.372%	$9.0017	$9.00	$9.00	$9.00
Purchase #7	$57.65	3.714%	$59.7911	$59.79	$59.80	$59.80
7 purchase totals =	$618.53		$667.8556	$667.86	$667.85	$667.90