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	$10.89	8.629%	$11.8297	$11.83	$11.85	$11.80
Purchase #2	$33.85	5.120%	$35.5831	$35.58	$35.60	$35.60
Purchase #3	$58.82	9.868%	$64.6244	$64.62	$64.60	$64.60
Purchase #4	$5.53	5.764%	$5.8487	$5.85	$5.85	$5.80
Purchase #5	$181.35	3.419%	$187.5504	$187.55	$187.55	$187.60
Purchase #6	$185.79	11.355%	$206.8865	$206.89	$206.90	$206.90
Purchase #7	$142.57	5.538%	$150.4655	$150.47	$150.45	$150.50
7 purchase totals =	$618.80		$662.7883	$662.79	$662.80	$662.80