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	$7.67	5.428%	$8.0863	$8.09	$8.10	$8.10
Purchase #2	$62.78	7.574%	$67.535	$67.54	$67.55	$67.50
Purchase #3	$19.96	4.127%	$20.7837	$20.78	$20.80	$20.80
Purchase #4	$39.31	4.592%	$41.1151	$41.12	$41.10	$41.10
Purchase #5	$126.82	8.726%	$137.8863	$137.89	$137.90	$137.90
Purchase #6	$199.93	4.298%	$208.523	$208.52	$208.50	$208.50
Purchase #7	$119.41	7.728%	$128.638	$128.64	$128.65	$128.60
7 purchase totals =	$575.88		$612.5674	$612.58	$612.60	$612.50