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	$185.99	12.452%	$209.1495	$209.15	$209.15	$209.10
Purchase #2	$178.95	6.330%	$190.2775	$190.28	$190.30	$190.30
Purchase #3	$87.61	13.757%	$99.6625	$99.66	$99.65	$99.70
Purchase #4	$36.31	6.257%	$38.5819	$38.58	$38.60	$38.60
Purchase #5	$161.79	10.662%	$179.04	$179.04	$179.05	$179.00
Purchase #6	$175.27	13.824%	$199.4993	$199.50	$199.50	$199.50
Purchase #7	$75.25	6.804%	$80.37	$80.37	$80.35	$80.40
7 purchase totals =	$901.17		$996.5807	$996.58	$996.60	$996.60