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	$126.38	8.609%	$137.2601	$137.26	$137.25	$137.30
Purchase #2	$134.48	4.560%	$140.6123	$140.61	$140.60	$140.60
Purchase #3	$170.40	12.171%	$191.1394	$191.14	$191.15	$191.10
Purchase #4	$119.99	5.145%	$126.1635	$126.16	$126.15	$126.20
Purchase #5	$218.72	5.728%	$231.2483	$231.25	$231.25	$231.20
Purchase #6	$59.58	11.597%	$66.4895	$66.49	$66.50	$66.50
Purchase #7	$99.53	3.869%	$103.3808	$103.38	$103.40	$103.40
7 purchase totals =	$929.08		$996.2939	$996.29	$996.30	$996.30