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	$84.61	4.321%	$88.266	$88.27	$88.25	$88.30
Purchase #2	$240.90	10.672%	$266.6088	$266.61	$266.60	$266.60
Purchase #3	$86.62	4.140%	$90.2061	$90.21	$90.20	$90.20
Purchase #4	$90.34	8.564%	$98.0767	$98.08	$98.10	$98.10
Purchase #5	$38.68	9.280%	$42.2695	$42.27	$42.25	$42.30
Purchase #6	$246.96	5.788%	$261.254	$261.25	$261.25	$261.30
Purchase #7	$47.74	4.336%	$49.81	$49.81	$49.80	$49.80
7 purchase totals =	$835.85		$896.4911	$896.50	$896.45	$896.60