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	$218.45	5.219%	$229.8509	$229.85	$229.85	$229.90
Purchase #2	$83.70	7.485%	$89.9649	$89.96	$89.95	$90.00
Purchase #3	$166.86	11.401%	$185.8837	$185.88	$185.90	$185.90
Purchase #4	$51.97	6.775%	$55.491	$55.49	$55.50	$55.50
Purchase #5	$69.81	10.801%	$77.3502	$77.35	$77.35	$77.40
Purchase #6	$29.92	5.380%	$31.5297	$31.53	$31.55	$31.50
Purchase #7	$174.69	9.264%	$190.8733	$190.87	$190.85	$190.90
7 purchase totals =	$795.40		$860.9437	$860.93	$860.95	$861.10