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	$189.98	3.391%	$196.4222	$196.42	$196.40	$196.40
Purchase #2	$181.43	10.413%	$200.3223	$200.32	$200.30	$200.30
Purchase #3	$136.63	5.630%	$144.3223	$144.32	$144.30	$144.30
Purchase #4	$143.60	6.295%	$152.6396	$152.64	$152.65	$152.60
Purchase #5	$28.37	5.384%	$29.8974	$29.90	$29.90	$29.90
Purchase #6	$125.42	12.252%	$140.7865	$140.79	$140.80	$140.80
Purchase #7	$240.61	8.672%	$261.4757	$261.48	$261.50	$261.50
7 purchase totals =	$1,046.04		$1,125.8660	$1,125.87	$1,125.85	$1,125.80