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	$80.43	12.703%	$90.647	$90.65	$90.65	$90.60
Purchase #2	$165.55	12.255%	$185.8382	$185.84	$185.85	$185.80
Purchase #3	$152.51	4.771%	$159.7863	$159.79	$159.80	$159.80
Purchase #4	$170.27	3.696%	$176.5632	$176.56	$176.55	$176.60
Purchase #5	$204.34	13.448%	$231.8196	$231.82	$231.80	$231.80
Purchase #6	$237.79	5.251%	$250.2764	$250.28	$250.30	$250.30
Purchase #7	$24.34	5.401%	$25.6546	$25.65	$25.65	$25.70
7 purchase totals =	$1,035.23		$1,120.5853	$1,120.59	$1,120.60	$1,120.60