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	$88.64	13.837%	$100.9051	$100.91	$100.90	$100.90
Purchase #2	$155.92	12.312%	$175.1169	$175.12	$175.10	$175.10
Purchase #3	$99.59	3.652%	$103.227	$103.23	$103.25	$103.20
Purchase #4	$80.31	12.135%	$90.0556	$90.06	$90.05	$90.10
Purchase #5	$62.81	3.368%	$64.9254	$64.93	$64.95	$64.90
Purchase #6	$158.97	6.869%	$169.8896	$169.89	$169.90	$169.90
Purchase #7	$37.60	11.240%	$41.8262	$41.83	$41.85	$41.80
7 purchase totals =	$683.84		$745.9458	$745.97	$746.00	$745.90