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	$40.63	3.471%	$42.0403	$42.04	$42.05	$42.00
Purchase #2	$106.74	13.215%	$120.8457	$120.85	$120.85	$120.80
Purchase #3	$49.89	7.517%	$53.6402	$53.64	$53.65	$53.60
Purchase #4	$52.63	12.380%	$59.1456	$59.15	$59.15	$59.10
Purchase #5	$32.68	4.299%	$34.0849	$34.08	$34.10	$34.10
Purchase #6	$87.57	9.171%	$95.601	$95.60	$95.60	$95.60
Purchase #7	$115.76	13.715%	$131.6365	$131.64	$131.65	$131.60
7 purchase totals =	$485.90		$536.9942	$537.00	$537.05	$536.80