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	$79.81	3.555%	$82.6472	$82.65	$82.65	$82.60
Purchase #2	$57.54	11.305%	$64.0449	$64.04	$64.05	$64.00
Purchase #3	$38.46	4.452%	$40.1722	$40.17	$40.15	$40.20
Purchase #4	$214.30	3.399%	$221.5841	$221.58	$221.60	$221.60
Purchase #5	$47.75	8.660%	$51.8852	$51.89	$51.90	$51.90
Purchase #6	$166.76	9.460%	$182.5355	$182.54	$182.55	$182.50
Purchase #7	$185.59	5.860%	$196.4656	$196.47	$196.45	$196.50
7 purchase totals =	$790.21		$839.3347	$839.34	$839.35	$839.30