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	$123.52	11.392%	$137.5914	$137.59	$137.60	$137.60
Purchase #2	$235.53	8.300%	$255.079	$255.08	$255.10	$255.10
Purchase #3	$228.53	12.110%	$256.205	$256.21	$256.20	$256.20
Purchase #4	$24.43	8.859%	$26.5943	$26.59	$26.60	$26.60
Purchase #5	$45.84	11.132%	$50.9429	$50.94	$50.95	$50.90
Purchase #6	$73.31	6.779%	$78.2797	$78.28	$78.30	$78.30
Purchase #7	$25.68	5.403%	$27.0675	$27.07	$27.05	$27.10
7 purchase totals =	$756.84		$831.7598	$831.76	$831.80	$831.80