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	$38.95	8.760%	$42.362	$42.36	$42.35	$42.40
Purchase #2	$66.30	4.156%	$69.0554	$69.06	$69.05	$69.10
Purchase #3	$57.67	7.190%	$61.8165	$61.82	$61.80	$61.80
Purchase #4	$129.60	12.288%	$145.5252	$145.53	$145.55	$145.50
Purchase #5	$238.84	9.641%	$261.8666	$261.87	$261.85	$261.90
Purchase #6	$139.40	11.303%	$155.1564	$155.16	$155.15	$155.20
Purchase #7	$122.61	7.563%	$131.883	$131.88	$131.90	$131.90
7 purchase totals =	$793.37		$867.6651	$867.68	$867.65	$867.80