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	$21.56	10.577%	$23.8404	$23.84	$23.85	$23.80
Purchase #2	$115.58	6.808%	$123.4487	$123.45	$123.45	$123.40
Purchase #3	$171.69	6.759%	$183.2945	$183.29	$183.30	$183.30
Purchase #4	$104.49	4.385%	$109.0719	$109.07	$109.05	$109.10
Purchase #5	$118.38	13.352%	$134.1861	$134.19	$134.20	$134.20
Purchase #6	$196.94	9.835%	$216.309	$216.31	$216.30	$216.30
Purchase #7	$35.25	13.800%	$40.1145	$40.11	$40.10	$40.10
7 purchase totals =	$763.89		$830.2651	$830.26	$830.25	$830.20