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	$83.82	7.727%	$90.2968	$90.30	$90.30	$90.30
Purchase #2	$248.84	6.259%	$264.4149	$264.41	$264.40	$264.40
Purchase #3	$210.57	3.841%	$218.658	$218.66	$218.65	$218.70
Purchase #4	$84.96	10.105%	$93.5452	$93.55	$93.55	$93.50
Purchase #5	$7.89	6.192%	$8.3785	$8.38	$8.40	$8.40
Purchase #6	$115.45	11.276%	$128.4681	$128.47	$128.45	$128.50
Purchase #7	$85.70	5.655%	$90.5463	$90.55	$90.55	$90.50
7 purchase totals =	$837.23		$894.3078	$894.32	$894.30	$894.30