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	$189.50	5.817%	$200.5232	$200.52	$200.50	$200.50
Purchase #2	$65.93	8.335%	$71.4253	$71.43	$71.45	$71.40
Purchase #3	$58.25	12.692%	$65.6431	$65.64	$65.65	$65.60
Purchase #4	$87.54	12.556%	$98.5315	$98.53	$98.55	$98.50
Purchase #5	$73.34	10.175%	$80.8023	$80.80	$80.80	$80.80
Purchase #6	$55.73	4.267%	$58.108	$58.11	$58.10	$58.10
Purchase #7	$215.61	12.523%	$242.6108	$242.61	$242.60	$242.60
7 purchase totals =	$745.90		$817.6442	$817.64	$817.65	$817.50