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	$24.88	13.678%	$28.2831	$28.28	$28.30	$28.30
Purchase #2	$186.56	11.791%	$208.5573	$208.56	$208.55	$208.60
Purchase #3	$134.65	4.397%	$140.5706	$140.57	$140.55	$140.60
Purchase #4	$30.36	3.625%	$31.4606	$31.46	$31.45	$31.50
Purchase #5	$196.52	4.857%	$206.065	$206.07	$206.05	$206.10
Purchase #6	$55.62	6.710%	$59.3521	$59.35	$59.35	$59.40
Purchase #7	$181.75	6.856%	$194.2108	$194.21	$194.20	$194.20
7 purchase totals =	$810.34		$868.4995	$868.50	$868.45	$868.70