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	$9.77	5.627%	$10.3198	$10.32	$10.30	$10.30
Purchase #2	$44.53	3.171%	$45.942	$45.94	$45.95	$45.90
Purchase #3	$177.52	4.111%	$184.8178	$184.82	$184.80	$184.80
Purchase #4	$33.98	13.282%	$38.4932	$38.49	$38.50	$38.50
Purchase #5	$91.63	13.412%	$103.9194	$103.92	$103.90	$103.90
Purchase #6	$13.42	12.831%	$15.1419	$15.14	$15.15	$15.10
Purchase #7	$190.68	4.262%	$198.8068	$198.81	$198.80	$198.80
7 purchase totals =	$561.53		$597.4409	$597.44	$597.40	$597.30