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	$109.43	5.315%	$115.2462	$115.25	$115.25	$115.20
Purchase #2	$198.38	3.179%	$204.6865	$204.69	$204.70	$204.70
Purchase #3	$144.49	13.726%	$164.3227	$164.32	$164.30	$164.30
Purchase #4	$28.25	4.735%	$29.5876	$29.59	$29.60	$29.60
Purchase #5	$155.27	11.158%	$172.595	$172.60	$172.60	$172.60
Purchase #6	$166.35	5.514%	$175.5225	$175.52	$175.50	$175.50
Purchase #7	$17.33	5.789%	$18.3332	$18.33	$18.35	$18.30
7 purchase totals =	$819.50		$880.2937	$880.30	$880.30	$880.20