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	$74.74	11.767%	$83.5347	$83.53	$83.55	$83.50
Purchase #2	$97.82	10.450%	$108.0422	$108.04	$108.05	$108.00
Purchase #3	$35.85	9.708%	$39.3303	$39.33	$39.35	$39.30
Purchase #4	$102.91	6.621%	$109.7237	$109.72	$109.70	$109.70
Purchase #5	$5.52	4.756%	$5.7825	$5.78	$5.80	$5.80
Purchase #6	$227.94	12.603%	$256.6673	$256.67	$256.65	$256.70
Purchase #7	$131.79	4.127%	$137.229	$137.23	$137.25	$137.20
7 purchase totals =	$676.57		$740.3097	$740.30	$740.35	$740.20