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	$34.39	6.473%	$36.6161	$36.62	$36.60	$36.60
Purchase #2	$39.59	6.339%	$42.0996	$42.10	$42.10	$42.10
Purchase #3	$18.61	12.494%	$20.9351	$20.94	$20.95	$20.90
Purchase #4	$125.56	4.364%	$131.0394	$131.04	$131.05	$131.00
Purchase #5	$237.83	6.378%	$252.9988	$253.00	$253.00	$253.00
Purchase #6	$28.63	6.154%	$30.3919	$30.39	$30.40	$30.40
Purchase #7	$98.43	13.644%	$111.8598	$111.86	$111.85	$111.90
7 purchase totals =	$583.04		$625.9407	$625.95	$625.95	$625.90