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	$220.70	13.677%	$250.8851	$250.89	$250.90	$250.90
Purchase #2	$204.47	13.127%	$231.3108	$231.31	$231.30	$231.30
Purchase #3	$40.25	6.379%	$42.8175	$42.82	$42.80	$42.80
Purchase #4	$49.69	4.165%	$51.7596	$51.76	$51.75	$51.80
Purchase #5	$119.72	5.146%	$125.8808	$125.88	$125.90	$125.90
Purchase #6	$246.51	3.206%	$254.4131	$254.41	$254.40	$254.40
Purchase #7	$66.97	11.176%	$74.4546	$74.45	$74.45	$74.50
7 purchase totals =	$948.31		$1,031.5215	$1,031.52	$1,031.50	$1,031.60