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	$123.64	3.573%	$128.0577	$128.06	$128.05	$128.10
Purchase #2	$43.55	5.388%	$45.8965	$45.90	$45.90	$45.90
Purchase #3	$218.46	12.205%	$245.123	$245.12	$245.10	$245.10
Purchase #4	$206.75	10.222%	$227.884	$227.88	$227.90	$227.90
Purchase #5	$11.83	13.238%	$13.3961	$13.40	$13.40	$13.40
Purchase #6	$239.43	11.199%	$266.2438	$266.24	$266.25	$266.20
Purchase #7	$108.61	4.354%	$113.3389	$113.34	$113.35	$113.30
7 purchase totals =	$952.27		$1,039.9400	$1,039.94	$1,039.95	$1,039.90