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	$32.31	13.429%	$36.6489	$36.65	$36.65	$36.60
Purchase #2	$231.41	10.450%	$255.5923	$255.59	$255.60	$255.60
Purchase #3	$51.67	8.164%	$55.8883	$55.89	$55.90	$55.90
Purchase #4	$136.35	11.647%	$152.2307	$152.23	$152.25	$152.20
Purchase #5	$195.82	6.813%	$209.1612	$209.16	$209.15	$209.20
Purchase #6	$120.31	4.686%	$125.9477	$125.95	$125.95	$125.90
Purchase #7	$92.42	6.632%	$98.5493	$98.55	$98.55	$98.50
7 purchase totals =	$860.29		$934.0184	$934.02	$934.05	$933.90