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	$146.71	9.274%	$160.3159	$160.32	$160.30	$160.30
Purchase #2	$236.68	11.599%	$264.1325	$264.13	$264.15	$264.10
Purchase #3	$143.37	10.162%	$157.9393	$157.94	$157.95	$157.90
Purchase #4	$23.67	7.669%	$25.4853	$25.49	$25.50	$25.50
Purchase #5	$68.95	4.745%	$72.2217	$72.22	$72.20	$72.20
Purchase #6	$48.74	13.210%	$55.1786	$55.18	$55.20	$55.20
Purchase #7	$70.77	11.316%	$78.7783	$78.78	$78.80	$78.80
7 purchase totals =	$738.89		$814.0516	$814.06	$814.10	$814.00