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	$45.57	8.536%	$49.4599	$49.46	$49.45	$49.50
Purchase #2	$133.87	13.873%	$152.4418	$152.44	$152.45	$152.40
Purchase #3	$89.55	5.799%	$94.743	$94.74	$94.75	$94.70
Purchase #4	$232.89	13.195%	$263.6198	$263.62	$263.60	$263.60
Purchase #5	$217.85	4.422%	$227.4833	$227.48	$227.50	$227.50
Purchase #6	$41.47	3.756%	$43.0276	$43.03	$43.05	$43.00
Purchase #7	$196.40	6.423%	$209.0148	$209.01	$209.00	$209.00
7 purchase totals =	$957.60		$1,039.7902	$1,039.78	$1,039.80	$1,039.70