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	$54.28	9.243%	$59.2971	$59.30	$59.30	$59.30
Purchase #2	$52.96	7.375%	$56.8658	$56.87	$56.85	$56.90
Purchase #3	$23.69	4.189%	$24.6824	$24.68	$24.70	$24.70
Purchase #4	$243.93	9.450%	$266.9814	$266.98	$267.00	$267.00
Purchase #5	$151.82	8.507%	$164.7353	$164.74	$164.75	$164.70
Purchase #6	$131.78	8.432%	$142.8917	$142.89	$142.90	$142.90
Purchase #7	$112.40	9.665%	$123.2635	$123.26	$123.25	$123.30
7 purchase totals =	$770.86		$838.7172	$838.72	$838.75	$838.80