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	$6.77	3.798%	$7.0271	$7.03	$7.05	$7.00
Purchase #2	$224.67	11.201%	$249.8353	$249.84	$249.85	$249.80
Purchase #3	$170.64	9.694%	$187.1818	$187.18	$187.20	$187.20
Purchase #4	$68.38	4.443%	$71.4181	$71.42	$71.40	$71.40
Purchase #5	$78.73	13.841%	$89.627	$89.63	$89.65	$89.60
Purchase #6	$210.35	3.704%	$218.1414	$218.14	$218.15	$218.10
Purchase #7	$142.32	11.614%	$158.849	$158.85	$158.85	$158.80
7 purchase totals =	$901.86		$982.0797	$982.09	$982.15	$981.90