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	$148.96	13.311%	$168.7881	$168.79	$168.80	$168.80
Purchase #2	$34.31	7.735%	$36.9639	$36.96	$36.95	$37.00
Purchase #3	$178.85	6.558%	$190.579	$190.58	$190.60	$190.60
Purchase #4	$44.51	11.270%	$49.5263	$49.53	$49.55	$49.50
Purchase #5	$69.44	6.473%	$73.9349	$73.93	$73.95	$73.90
Purchase #6	$85.34	4.331%	$89.0361	$89.04	$89.05	$89.00
Purchase #7	$52.59	7.477%	$56.5222	$56.52	$56.50	$56.50
7 purchase totals =	$614.00		$665.3505	$665.35	$665.40	$665.30