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	$221.79	3.642%	$229.8676	$229.87	$229.85	$229.90
Purchase #2	$29.83	8.495%	$32.3641	$32.36	$32.35	$32.40
Purchase #3	$28.61	9.840%	$31.4252	$31.43	$31.45	$31.40
Purchase #4	$175.28	11.394%	$195.2514	$195.25	$195.25	$195.30
Purchase #5	$71.48	7.329%	$76.7188	$76.72	$76.70	$76.70
Purchase #6	$137.32	4.433%	$143.4074	$143.41	$143.40	$143.40
Purchase #7	$28.93	9.275%	$31.6133	$31.61	$31.60	$31.60
7 purchase totals =	$693.24		$740.6478	$740.65	$740.60	$740.70