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	$48.86	9.200%	$53.3551	$53.36	$53.35	$53.40
Purchase #2	$134.49	10.199%	$148.2066	$148.21	$148.20	$148.20
Purchase #3	$34.43	8.705%	$37.4271	$37.43	$37.45	$37.40
Purchase #4	$123.79	6.379%	$131.6866	$131.69	$131.70	$131.70
Purchase #5	$129.90	6.141%	$137.8772	$137.88	$137.90	$137.90
Purchase #6	$59.26	12.576%	$66.7125	$66.71	$66.70	$66.70
Purchase #7	$76.64	5.727%	$81.0292	$81.03	$81.05	$81.00
7 purchase totals =	$607.37		$656.2943	$656.31	$656.35	$656.30