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	$81.73	9.857%	$89.7861	$89.79	$89.80	$89.80
Purchase #2	$173.77	10.517%	$192.0454	$192.05	$192.05	$192.00
Purchase #3	$84.97	5.677%	$89.7937	$89.79	$89.80	$89.80
Purchase #4	$212.95	11.297%	$237.007	$237.01	$237.00	$237.00
Purchase #5	$228.73	13.211%	$258.9475	$258.95	$258.95	$258.90
Purchase #6	$85.41	5.413%	$90.0332	$90.03	$90.05	$90.00
Purchase #7	$90.45	5.622%	$95.5351	$95.54	$95.55	$95.50
7 purchase totals =	$958.01		$1,053.1480	$1,053.16	$1,053.20	$1,053.00