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	$32.97	6.386%	$35.0755	$35.08	$35.10	$35.10
Purchase #2	$29.41	5.660%	$31.0746	$31.07	$31.05	$31.10
Purchase #3	$163.48	11.489%	$182.2622	$182.26	$182.25	$182.30
Purchase #4	$140.54	4.288%	$146.5664	$146.57	$146.55	$146.60
Purchase #5	$44.75	10.794%	$49.5803	$49.58	$49.60	$49.60
Purchase #6	$136.56	4.338%	$142.484	$142.48	$142.50	$142.50
Purchase #7	$53.38	11.673%	$59.611	$59.61	$59.60	$59.60
7 purchase totals =	$601.09		$646.6540	$646.65	$646.65	$646.80