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	$100.71	12.571%	$113.3703	$113.37	$113.35	$113.40
Purchase #2	$127.90	12.557%	$143.9604	$143.96	$143.95	$144.00
Purchase #3	$167.50	12.516%	$188.4643	$188.46	$188.45	$188.50
Purchase #4	$150.49	4.496%	$157.256	$157.26	$157.25	$157.30
Purchase #5	$117.44	5.492%	$123.8898	$123.89	$123.90	$123.90
Purchase #6	$89.85	7.750%	$96.8134	$96.81	$96.80	$96.80
Purchase #7	$119.50	9.767%	$131.1716	$131.17	$131.15	$131.20
7 purchase totals =	$873.39		$954.9258	$954.92	$954.85	$955.10