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	$102.85	6.680%	$109.7204	$109.72	$109.70	$109.70
Purchase #2	$192.32	4.140%	$200.282	$200.28	$200.30	$200.30
Purchase #3	$102.25	10.864%	$113.3584	$113.36	$113.35	$113.40
Purchase #4	$34.53	8.812%	$37.5728	$37.57	$37.55	$37.60
Purchase #5	$99.76	3.149%	$102.9014	$102.90	$102.90	$102.90
Purchase #6	$17.47	4.779%	$18.3049	$18.30	$18.30	$18.30
Purchase #7	$121.54	4.555%	$127.0761	$127.08	$127.10	$127.10
7 purchase totals =	$670.72		$709.2160	$709.21	$709.20	$709.30