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	$81.36	12.751%	$91.7342	$91.73	$91.75	$91.70
Purchase #2	$136.48	3.628%	$141.4315	$141.43	$141.45	$141.40
Purchase #3	$230.89	12.434%	$259.5989	$259.60	$259.60	$259.60
Purchase #4	$28.91	12.159%	$32.4252	$32.43	$32.45	$32.40
Purchase #5	$47.91	6.236%	$50.8977	$50.90	$50.90	$50.90
Purchase #6	$37.74	4.796%	$39.55	$39.55	$39.55	$39.60
Purchase #7	$219.77	6.238%	$233.4793	$233.48	$233.50	$233.50
7 purchase totals =	$783.06		$849.1168	$849.12	$849.20	$849.10