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	$58.79	12.463%	$66.117	$66.12	$66.10	$66.10
Purchase #2	$209.53	13.169%	$237.123	$237.12	$237.10	$237.10
Purchase #3	$27.89	13.868%	$31.7578	$31.76	$31.75	$31.80
Purchase #4	$78.65	12.444%	$88.4372	$88.44	$88.45	$88.40
Purchase #5	$185.66	7.602%	$199.7739	$199.77	$199.75	$199.80
Purchase #6	$224.72	3.730%	$233.1021	$233.10	$233.10	$233.10
Purchase #7	$116.26	13.226%	$131.6365	$131.64	$131.65	$131.60
7 purchase totals =	$901.50		$987.9475	$987.95	$987.90	$987.90