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	$136.45	6.207%	$144.9195	$144.92	$144.90	$144.90
Purchase #2	$34.32	9.347%	$37.5279	$37.53	$37.55	$37.50
Purchase #3	$219.32	6.486%	$233.5451	$233.55	$233.55	$233.50
Purchase #4	$250.53	8.500%	$271.8251	$271.83	$271.85	$271.80
Purchase #5	$216.98	8.574%	$235.5839	$235.58	$235.60	$235.60
Purchase #6	$11.39	10.734%	$12.6126	$12.61	$12.60	$12.60
Purchase #7	$24.48	4.618%	$25.6105	$25.61	$25.60	$25.60
7 purchase totals =	$893.47		$961.6246	$961.63	$961.65	$961.50