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	$86.64	5.671%	$91.5534	$91.55	$91.55	$91.60
Purchase #2	$109.68	13.631%	$124.6305	$124.63	$124.65	$124.60
Purchase #3	$121.81	11.799%	$136.1824	$136.18	$136.20	$136.20
Purchase #4	$61.34	10.167%	$67.5764	$67.58	$67.60	$67.60
Purchase #5	$137.63	10.394%	$151.9353	$151.94	$151.95	$151.90
Purchase #6	$106.90	7.197%	$114.5936	$114.59	$114.60	$114.60
Purchase #7	$134.98	5.482%	$142.3796	$142.38	$142.40	$142.40
7 purchase totals =	$758.98		$828.8512	$828.85	$828.95	$828.90