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	$84.51	11.799%	$94.4813	$94.48	$94.50	$94.50
Purchase #2	$206.73	7.650%	$222.5448	$222.54	$222.55	$222.50
Purchase #3	$56.93	8.606%	$61.8294	$61.83	$61.85	$61.80
Purchase #4	$134.48	3.615%	$139.3415	$139.34	$139.35	$139.30
Purchase #5	$140.99	6.130%	$149.6327	$149.63	$149.65	$149.60
Purchase #6	$136.54	4.449%	$142.6147	$142.61	$142.60	$142.60
Purchase #7	$101.56	3.798%	$105.4172	$105.42	$105.40	$105.40
7 purchase totals =	$861.74		$915.8616	$915.85	$915.90	$915.70