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	$19.39	3.220%	$20.0144	$20.01	$20.00	$20.00
Purchase #2	$103.49	8.402%	$112.1852	$112.19	$112.20	$112.20
Purchase #3	$175.48	13.316%	$198.8469	$198.85	$198.85	$198.80
Purchase #4	$191.90	13.520%	$217.8449	$217.84	$217.85	$217.80
Purchase #5	$54.96	8.304%	$59.5239	$59.52	$59.50	$59.50
Purchase #6	$128.38	4.711%	$134.428	$134.43	$134.45	$134.40
Purchase #7	$66.65	10.372%	$73.5629	$73.56	$73.55	$73.60
7 purchase totals =	$740.25		$816.4062	$816.40	$816.40	$816.30