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	$244.44	11.690%	$273.015	$273.02	$273.00	$273.00
Purchase #2	$146.33	4.167%	$152.4276	$152.43	$152.45	$152.40
Purchase #3	$189.88	3.793%	$197.0821	$197.08	$197.10	$197.10
Purchase #4	$21.92	11.534%	$24.4483	$24.45	$24.45	$24.40
Purchase #5	$109.60	3.460%	$113.3922	$113.39	$113.40	$113.40
Purchase #6	$160.51	9.586%	$175.8965	$175.90	$175.90	$175.90
Purchase #7	$131.64	9.804%	$144.546	$144.55	$144.55	$144.50
7 purchase totals =	$1,004.32		$1,080.8077	$1,080.82	$1,080.85	$1,080.70