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	$6.66	12.237%	$7.475	$7.48	$7.50	$7.50
Purchase #2	$78.88	9.619%	$86.4675	$86.47	$86.45	$86.50
Purchase #3	$46.87	12.703%	$52.8239	$52.82	$52.80	$52.80
Purchase #4	$50.89	8.705%	$55.32	$55.32	$55.30	$55.30
Purchase #5	$249.89	9.436%	$273.4696	$273.47	$273.45	$273.50
Purchase #6	$205.39	6.360%	$218.4528	$218.45	$218.45	$218.50
Purchase #7	$234.92	9.573%	$257.4089	$257.41	$257.40	$257.40
7 purchase totals =	$873.50		$951.4177	$951.42	$951.35	$951.50