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	$22.51	9.427%	$24.632	$24.63	$24.65	$24.60
Purchase #2	$242.48	3.177%	$250.1836	$250.18	$250.20	$250.20
Purchase #3	$107.87	8.766%	$117.3259	$117.33	$117.35	$117.30
Purchase #4	$246.63	3.642%	$255.6123	$255.61	$255.60	$255.60
Purchase #5	$85.76	8.247%	$92.8326	$92.83	$92.85	$92.80
Purchase #6	$140.61	11.331%	$156.5425	$156.54	$156.55	$156.50
Purchase #7	$37.86	4.215%	$39.4558	$39.46	$39.45	$39.50
7 purchase totals =	$883.72		$936.5847	$936.58	$936.65	$936.50