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	$31.47	4.408%	$32.8572	$32.86	$32.85	$32.90
Purchase #2	$130.32	5.127%	$137.0015	$137.00	$137.00	$137.00
Purchase #3	$169.76	13.114%	$192.0223	$192.02	$192.00	$192.00
Purchase #4	$132.70	5.250%	$139.6668	$139.67	$139.65	$139.70
Purchase #5	$61.38	10.264%	$67.68	$67.68	$67.70	$67.70
Purchase #6	$76.94	11.402%	$85.7127	$85.71	$85.70	$85.70
Purchase #7	$28.80	10.511%	$31.8272	$31.83	$31.85	$31.80
7 purchase totals =	$631.37		$686.7677	$686.77	$686.75	$686.80