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	$140.75	3.249%	$145.323	$145.32	$145.30	$145.30
Purchase #2	$145.31	3.548%	$150.4656	$150.47	$150.45	$150.50
Purchase #3	$64.73	13.674%	$73.5812	$73.58	$73.60	$73.60
Purchase #4	$99.78	12.357%	$112.1098	$112.11	$112.10	$112.10
Purchase #5	$89.91	3.128%	$92.7224	$92.72	$92.70	$92.70
Purchase #6	$32.93	7.121%	$35.2749	$35.27	$35.25	$35.30
Purchase #7	$27.79	13.429%	$31.5219	$31.52	$31.50	$31.50
7 purchase totals =	$601.20		$640.9988	$640.99	$640.90	$641.00