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	$79.83	13.677%	$90.7483	$90.75	$90.75	$90.70
Purchase #2	$137.50	3.791%	$142.7126	$142.71	$142.70	$142.70
Purchase #3	$90.97	9.503%	$99.6149	$99.61	$99.60	$99.60
Purchase #4	$180.66	8.642%	$196.2726	$196.27	$196.25	$196.30
Purchase #5	$201.90	11.545%	$225.2094	$225.21	$225.20	$225.20
Purchase #6	$77.38	10.696%	$85.6566	$85.66	$85.65	$85.70
Purchase #7	$80.52	7.651%	$86.6806	$86.68	$86.70	$86.70
7 purchase totals =	$848.76		$926.8950	$926.89	$926.85	$926.90