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	$138.41	13.510%	$157.1092	$157.11	$157.10	$157.10
Purchase #2	$200.65	9.533%	$219.778	$219.78	$219.80	$219.80
Purchase #3	$106.81	4.570%	$111.6912	$111.69	$111.70	$111.70
Purchase #4	$180.93	10.479%	$199.8897	$199.89	$199.90	$199.90
Purchase #5	$96.58	7.658%	$103.9761	$103.98	$104.00	$104.00
Purchase #6	$126.80	8.730%	$137.8696	$137.87	$137.85	$137.90
Purchase #7	$86.92	10.282%	$95.8571	$95.86	$95.85	$95.90
7 purchase totals =	$937.10		$1,026.1709	$1,026.18	$1,026.20	$1,026.30