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	$33.50	6.444%	$35.6587	$35.66	$35.65	$35.70
Purchase #2	$174.66	8.710%	$189.8729	$189.87	$189.85	$189.90
Purchase #3	$94.75	5.682%	$100.1337	$100.13	$100.15	$100.10
Purchase #4	$38.85	3.850%	$40.3457	$40.35	$40.35	$40.30
Purchase #5	$29.81	12.394%	$33.5047	$33.50	$33.50	$33.50
Purchase #6	$180.47	9.809%	$198.1723	$198.17	$198.15	$198.20
Purchase #7	$233.68	12.499%	$262.8877	$262.89	$262.90	$262.90
7 purchase totals =	$785.72		$860.5757	$860.57	$860.55	$860.60