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	$218.67	6.772%	$233.4783	$233.48	$233.50	$233.50
Purchase #2	$230.86	8.228%	$249.8552	$249.86	$249.85	$249.90
Purchase #3	$57.66	7.559%	$62.0185	$62.02	$62.00	$62.00
Purchase #4	$40.31	13.556%	$45.7744	$45.77	$45.75	$45.80
Purchase #5	$160.51	3.704%	$166.4553	$166.46	$166.45	$166.50
Purchase #6	$27.38	9.352%	$29.9406	$29.94	$29.95	$29.90
Purchase #7	$34.39	7.534%	$36.9809	$36.98	$37.00	$37.00
7 purchase totals =	$769.78		$824.5032	$824.51	$824.50	$824.60