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	$184.34	13.711%	$209.6149	$209.61	$209.60	$209.60
Purchase #2	$63.88	4.664%	$66.8594	$66.86	$66.85	$66.90
Purchase #3	$63.52	8.251%	$68.761	$68.76	$68.75	$68.80
Purchase #4	$58.82	11.600%	$65.6431	$65.64	$65.65	$65.60
Purchase #5	$136.89	3.256%	$141.3471	$141.35	$141.35	$141.30
Purchase #6	$61.76	7.239%	$66.2308	$66.23	$66.25	$66.20
Purchase #7	$211.52	13.704%	$240.5067	$240.51	$240.50	$240.50
7 purchase totals =	$780.73		$858.9630	$858.96	$858.95	$858.90