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	$40.42	6.145%	$42.9038	$42.90	$42.90	$42.90
Purchase #2	$236.93	4.712%	$248.0941	$248.09	$248.10	$248.10
Purchase #3	$79.41	13.748%	$90.3273	$90.33	$90.35	$90.30
Purchase #4	$103.98	8.858%	$113.1905	$113.19	$113.20	$113.20
Purchase #5	$93.45	10.745%	$103.4912	$103.49	$103.50	$103.50
Purchase #6	$124.95	10.715%	$138.3384	$138.34	$138.35	$138.30
Purchase #7	$175.39	8.342%	$190.021	$190.02	$190.00	$190.00
7 purchase totals =	$854.53		$926.3663	$926.36	$926.40	$926.30