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	$39.56	10.292%	$43.6315	$43.63	$43.65	$43.60
Purchase #2	$182.52	9.351%	$199.5874	$199.59	$199.60	$199.60
Purchase #3	$97.61	7.144%	$104.5833	$104.58	$104.60	$104.60
Purchase #4	$105.25	4.400%	$109.881	$109.88	$109.90	$109.90
Purchase #5	$86.98	5.261%	$91.556	$91.56	$91.55	$91.60
Purchase #6	$78.33	10.831%	$86.8139	$86.81	$86.80	$86.80
Purchase #7	$188.42	11.136%	$209.4025	$209.40	$209.40	$209.40
7 purchase totals =	$778.67		$845.4556	$845.45	$845.50	$845.50