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	$32.77	6.467%	$34.8892	$34.89	$34.90	$34.90
Purchase #2	$82.97	4.420%	$86.6373	$86.64	$86.65	$86.60
Purchase #3	$152.68	8.490%	$165.6425	$165.64	$165.65	$165.60
Purchase #4	$121.82	12.281%	$136.7807	$136.78	$136.80	$136.80
Purchase #5	$105.53	8.803%	$114.8198	$114.82	$114.80	$114.80
Purchase #6	$90.75	12.184%	$101.807	$101.81	$101.80	$101.80
Purchase #7	$172.65	10.844%	$191.3722	$191.37	$191.35	$191.40
7 purchase totals =	$759.17		$831.9487	$831.95	$831.95	$831.90