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	$64.89	3.580%	$67.2131	$67.21	$67.20	$67.20
Purchase #2	$93.77	5.754%	$99.1655	$99.17	$99.15	$99.20
Purchase #3	$115.85	10.712%	$128.2599	$128.26	$128.25	$128.30
Purchase #4	$215.29	11.853%	$240.8083	$240.81	$240.80	$240.80
Purchase #5	$133.79	3.839%	$138.9262	$138.93	$138.95	$138.90
Purchase #6	$183.50	13.838%	$208.8927	$208.89	$208.90	$208.90
Purchase #7	$65.62	10.221%	$72.327	$72.33	$72.35	$72.30
7 purchase totals =	$872.71		$955.5927	$955.60	$955.60	$955.60