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	$36.74	9.402%	$40.1943	$40.19	$40.20	$40.20
Purchase #2	$38.26	4.734%	$40.0712	$40.07	$40.05	$40.10
Purchase #3	$50.59	3.241%	$52.2296	$52.23	$52.25	$52.20
Purchase #4	$174.45	4.795%	$182.8149	$182.81	$182.80	$182.80
Purchase #5	$37.75	9.554%	$41.3566	$41.36	$41.35	$41.40
Purchase #6	$163.68	13.482%	$185.7473	$185.75	$185.75	$185.70
Purchase #7	$245.82	9.651%	$269.5441	$269.54	$269.55	$269.50
7 purchase totals =	$747.29		$811.9580	$811.95	$811.95	$811.90