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	$33.34	12.334%	$37.4522	$37.45	$37.45	$37.50
Purchase #2	$179.81	5.837%	$190.3055	$190.31	$190.30	$190.30
Purchase #3	$109.48	4.400%	$114.2971	$114.30	$114.30	$114.30
Purchase #4	$8.56	7.818%	$9.2292	$9.23	$9.25	$9.20
Purchase #5	$217.78	9.697%	$238.8981	$238.90	$238.90	$238.90
Purchase #6	$112.81	9.607%	$123.6477	$123.65	$123.65	$123.60
Purchase #7	$57.39	7.654%	$61.7826	$61.78	$61.80	$61.80
7 purchase totals =	$719.17		$775.6124	$775.62	$775.65	$775.60