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	$127.48	12.305%	$143.1664	$143.17	$143.15	$143.20
Purchase #2	$100.30	3.589%	$103.8998	$103.90	$103.90	$103.90
Purchase #3	$229.50	11.595%	$256.1105	$256.11	$256.10	$256.10
Purchase #4	$76.28	6.714%	$81.4014	$81.40	$81.40	$81.40
Purchase #5	$129.92	11.470%	$144.8218	$144.82	$144.80	$144.80
Purchase #6	$174.73	13.571%	$198.4426	$198.44	$198.45	$198.40
Purchase #7	$200.51	7.309%	$215.1653	$215.17	$215.15	$215.20
7 purchase totals =	$1,038.72		$1,143.0078	$1,143.01	$1,142.95	$1,143.00