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	$96.48	3.202%	$99.5693	$99.57	$99.55	$99.60
Purchase #2	$38.96	8.352%	$42.2139	$42.21	$42.20	$42.20
Purchase #3	$104.46	11.547%	$116.522	$116.52	$116.50	$116.50
Purchase #4	$33.33	11.790%	$37.2596	$37.26	$37.25	$37.30
Purchase #5	$82.68	9.417%	$90.466	$90.47	$90.45	$90.50
Purchase #6	$238.33	13.687%	$270.9502	$270.95	$270.95	$271.00
Purchase #7	$34.96	9.277%	$38.2032	$38.20	$38.20	$38.20
7 purchase totals =	$629.20		$695.1842	$695.18	$695.10	$695.30