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	$108.88	6.212%	$115.6436	$115.64	$115.65	$115.60
Purchase #2	$31.95	11.290%	$35.5572	$35.56	$35.55	$35.60
Purchase #3	$105.44	12.280%	$118.388	$118.39	$118.40	$118.40
Purchase #4	$242.88	3.320%	$250.9436	$250.94	$250.95	$250.90
Purchase #5	$51.65	10.405%	$57.0242	$57.02	$57.00	$57.00
Purchase #6	$69.52	4.412%	$72.5872	$72.59	$72.60	$72.60
Purchase #7	$247.28	8.149%	$267.4308	$267.43	$267.45	$267.40
7 purchase totals =	$857.60		$917.5746	$917.57	$917.60	$917.50