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	$5.26	11.323%	$5.8556	$5.86	$5.85	$5.90
Purchase #2	$144.62	5.540%	$152.6319	$152.63	$152.65	$152.60
Purchase #3	$109.47	8.274%	$118.5275	$118.53	$118.55	$118.50
Purchase #4	$185.44	12.596%	$208.798	$208.80	$208.80	$208.80
Purchase #5	$75.50	13.720%	$85.8586	$85.86	$85.85	$85.90
Purchase #6	$217.92	6.222%	$231.479	$231.48	$231.50	$231.50
Purchase #7	$98.76	4.667%	$103.3691	$103.37	$103.35	$103.40
7 purchase totals =	$836.97		$906.5197	$906.53	$906.55	$906.60