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	$76.60	4.257%	$79.8609	$79.86	$79.85	$79.90
Purchase #2	$86.71	5.601%	$91.5666	$91.57	$91.55	$91.60
Purchase #3	$36.34	11.380%	$40.4755	$40.48	$40.50	$40.50
Purchase #4	$209.30	9.367%	$228.9051	$228.91	$228.90	$228.90
Purchase #5	$30.38	7.470%	$32.6494	$32.65	$32.65	$32.60
Purchase #6	$74.89	9.119%	$81.7192	$81.72	$81.70	$81.70
Purchase #7	$174.83	7.178%	$187.3793	$187.38	$187.40	$187.40
7 purchase totals =	$689.05		$742.5560	$742.57	$742.55	$742.60