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	$63.70	12.287%	$71.5268	$71.53	$71.55	$71.50
Purchase #2	$100.52	5.281%	$105.8285	$105.83	$105.85	$105.80
Purchase #3	$187.81	11.805%	$209.981	$209.98	$210.00	$210.00
Purchase #4	$52.94	9.423%	$57.9285	$57.93	$57.95	$57.90
Purchase #5	$123.29	12.712%	$138.9626	$138.96	$138.95	$139.00
Purchase #6	$40.90	4.227%	$42.6288	$42.63	$42.65	$42.60
Purchase #7	$63.58	13.212%	$71.9802	$71.98	$72.00	$72.00
7 purchase totals =	$632.74		$698.8364	$698.84	$698.95	$698.80