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	$19.98	11.678%	$22.3133	$22.31	$22.30	$22.30
Purchase #2	$30.53	10.628%	$33.7747	$33.77	$33.75	$33.80
Purchase #3	$38.74	10.514%	$42.8131	$42.81	$42.80	$42.80
Purchase #4	$228.36	11.745%	$255.1809	$255.18	$255.20	$255.20
Purchase #5	$195.82	6.751%	$209.0398	$209.04	$209.05	$209.00
Purchase #6	$157.38	9.854%	$172.8882	$172.89	$172.90	$172.90
Purchase #7	$161.99	6.641%	$172.7478	$172.75	$172.75	$172.70
7 purchase totals =	$832.80		$908.7578	$908.75	$908.75	$908.70