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	$158.58	3.744%	$164.5172	$164.52	$164.50	$164.50
Purchase #2	$37.36	9.246%	$40.8143	$40.81	$40.80	$40.80
Purchase #3	$84.71	4.833%	$88.804	$88.80	$88.80	$88.80
Purchase #4	$200.76	8.447%	$217.7182	$217.72	$217.70	$217.70
Purchase #5	$35.83	13.254%	$40.5789	$40.58	$40.60	$40.60
Purchase #6	$128.94	7.452%	$138.5486	$138.55	$138.55	$138.50
Purchase #7	$81.31	11.811%	$90.9135	$90.91	$90.90	$90.90
7 purchase totals =	$727.49		$781.8947	$781.89	$781.85	$781.80