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	$33.98	11.533%	$37.8989	$37.90	$37.90	$37.90
Purchase #2	$179.80	11.121%	$199.7956	$199.80	$199.80	$199.80
Purchase #3	$69.91	12.237%	$78.4649	$78.46	$78.45	$78.50
Purchase #4	$6.72	3.491%	$6.9546	$6.95	$6.95	$7.00
Purchase #5	$45.66	13.766%	$51.9456	$51.95	$51.95	$51.90
Purchase #6	$143.70	13.352%	$162.8868	$162.89	$162.90	$162.90
Purchase #7	$200.99	7.531%	$216.1266	$216.13	$216.15	$216.10
7 purchase totals =	$680.76		$754.0730	$754.08	$754.10	$754.10