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	$186.86	11.798%	$208.9057	$208.91	$208.90	$208.90
Purchase #2	$200.56	13.797%	$228.2313	$228.23	$228.25	$228.20
Purchase #3	$44.61	5.145%	$46.9052	$46.91	$46.90	$46.90
Purchase #4	$7.73	6.650%	$8.244	$8.24	$8.25	$8.20
Purchase #5	$136.98	11.312%	$152.4752	$152.48	$152.50	$152.50
Purchase #6	$6.86	5.676%	$7.2494	$7.25	$7.25	$7.20
Purchase #7	$46.30	3.695%	$48.0108	$48.01	$48.00	$48.00
7 purchase totals =	$629.90		$700.0216	$700.03	$700.05	$699.90