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	$29.75	10.519%	$32.8794	$32.88	$32.90	$32.90
Purchase #2	$115.56	4.602%	$120.8781	$120.88	$120.90	$120.90
Purchase #3	$43.61	7.873%	$47.0434	$47.04	$47.05	$47.00
Purchase #4	$103.37	7.271%	$110.886	$110.89	$110.90	$110.90
Purchase #5	$205.82	8.306%	$222.9154	$222.92	$222.90	$222.90
Purchase #6	$91.74	12.540%	$103.2442	$103.24	$103.25	$103.20
Purchase #7	$51.84	12.475%	$58.307	$58.31	$58.30	$58.30
7 purchase totals =	$641.69		$696.1535	$696.16	$696.20	$696.10