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	$119.40	3.864%	$124.0136	$124.01	$124.00	$124.00
Purchase #2	$113.91	8.713%	$123.835	$123.84	$123.85	$123.80
Purchase #3	$100.87	8.180%	$109.1212	$109.12	$109.10	$109.10
Purchase #4	$139.62	3.626%	$144.6826	$144.68	$144.70	$144.70
Purchase #5	$79.47	8.725%	$86.4038	$86.40	$86.40	$86.40
Purchase #6	$142.37	10.290%	$157.0199	$157.02	$157.00	$157.00
Purchase #7	$81.82	10.732%	$90.6009	$90.60	$90.60	$90.60
7 purchase totals =	$777.46		$835.6770	$835.67	$835.65	$835.60