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	$40.72	7.551%	$43.7948	$43.79	$43.80	$43.80
Purchase #2	$247.76	10.495%	$273.7624	$273.76	$273.75	$273.80
Purchase #3	$246.70	4.464%	$257.7127	$257.71	$257.70	$257.70
Purchase #4	$133.63	12.640%	$150.5208	$150.52	$150.50	$150.50
Purchase #5	$23.70	5.342%	$24.9661	$24.97	$24.95	$25.00
Purchase #6	$134.85	3.262%	$139.2488	$139.25	$139.25	$139.20
Purchase #7	$74.36	12.813%	$83.8877	$83.89	$83.90	$83.90
7 purchase totals =	$901.72		$973.8933	$973.89	$973.85	$973.90