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	$73.83	8.548%	$80.141	$80.14	$80.15	$80.10
Purchase #2	$148.81	12.331%	$167.1598	$167.16	$167.15	$167.20
Purchase #3	$94.35	4.303%	$98.4099	$98.41	$98.40	$98.40
Purchase #4	$62.95	7.745%	$67.8255	$67.83	$67.85	$67.80
Purchase #5	$212.39	12.504%	$238.9472	$238.95	$238.95	$238.90
Purchase #6	$236.81	10.753%	$262.2742	$262.27	$262.25	$262.30
Purchase #7	$95.68	8.471%	$103.7851	$103.79	$103.80	$103.80
7 purchase totals =	$924.82		$1,018.5427	$1,018.55	$1,018.55	$1,018.50