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	$73.27	12.540%	$82.4581	$82.46	$82.45	$82.50
Purchase #2	$57.59	6.392%	$61.2712	$61.27	$61.25	$61.30
Purchase #3	$232.58	7.155%	$249.2211	$249.22	$249.20	$249.20
Purchase #4	$151.80	10.379%	$167.5553	$167.56	$167.55	$167.60
Purchase #5	$160.76	5.527%	$169.6452	$169.65	$169.65	$169.60
Purchase #6	$64.72	9.187%	$70.6658	$70.67	$70.65	$70.70
Purchase #7	$73.58	12.378%	$82.6877	$82.69	$82.70	$82.70
7 purchase totals =	$814.30		$883.5044	$883.52	$883.45	$883.60