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	$31.89	12.770%	$35.9624	$35.96	$35.95	$36.00
Purchase #2	$101.60	8.594%	$110.3315	$110.33	$110.35	$110.30
Purchase #3	$193.63	12.385%	$217.6111	$217.61	$217.60	$217.60
Purchase #4	$98.80	4.741%	$103.4841	$103.48	$103.50	$103.50
Purchase #5	$142.40	11.292%	$158.4798	$158.48	$158.50	$158.50
Purchase #6	$144.40	4.779%	$151.3009	$151.30	$151.30	$151.30
Purchase #7	$29.28	13.294%	$33.1725	$33.17	$33.15	$33.20
7 purchase totals =	$742.00		$810.3423	$810.33	$810.35	$810.40