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	$76.48	12.426%	$85.9834	$85.98	$86.00	$86.00
Purchase #2	$171.51	10.405%	$189.3556	$189.36	$189.35	$189.40
Purchase #3	$167.31	6.708%	$178.5332	$178.53	$178.55	$178.50
Purchase #4	$48.71	5.743%	$51.5074	$51.51	$51.50	$51.50
Purchase #5	$41.85	7.452%	$44.9687	$44.97	$44.95	$45.00
Purchase #6	$57.25	12.775%	$64.5637	$64.56	$64.55	$64.60
Purchase #7	$38.72	8.629%	$42.0611	$42.06	$42.05	$42.10
7 purchase totals =	$601.83		$656.9731	$656.97	$656.95	$657.10