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	$160.73	12.699%	$181.1411	$181.14	$181.15	$181.10
Purchase #2	$243.32	4.161%	$253.4445	$253.44	$253.45	$253.40
Purchase #3	$31.79	9.397%	$34.7773	$34.78	$34.80	$34.80
Purchase #4	$121.94	5.641%	$128.8186	$128.82	$128.80	$128.80
Purchase #5	$38.31	8.106%	$41.4154	$41.42	$41.40	$41.40
Purchase #6	$93.71	12.458%	$105.3844	$105.38	$105.40	$105.40
Purchase #7	$140.48	8.661%	$152.647	$152.65	$152.65	$152.60
7 purchase totals =	$830.28		$897.6283	$897.63	$897.65	$897.50