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	$19.67	9.364%	$21.5119	$21.51	$21.50	$21.50
Purchase #2	$149.60	5.291%	$157.5153	$157.52	$157.50	$157.50
Purchase #3	$90.51	9.371%	$98.9917	$98.99	$99.00	$99.00
Purchase #4	$174.77	10.369%	$192.8919	$192.89	$192.90	$192.90
Purchase #5	$39.38	5.298%	$41.4664	$41.47	$41.45	$41.50
Purchase #6	$137.73	12.386%	$154.7892	$154.79	$154.80	$154.80
Purchase #7	$81.68	11.748%	$91.2758	$91.28	$91.30	$91.30
7 purchase totals =	$693.34		$758.4422	$758.45	$758.45	$758.50