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	$18.43	7.777%	$19.8633	$19.86	$19.85	$19.90
Purchase #2	$59.72	4.372%	$62.331	$62.33	$62.35	$62.30
Purchase #3	$91.86	7.692%	$98.9259	$98.93	$98.95	$98.90
Purchase #4	$143.65	12.401%	$161.464	$161.46	$161.45	$161.50
Purchase #5	$35.92	3.640%	$37.2275	$37.23	$37.25	$37.20
Purchase #6	$187.62	5.836%	$198.5695	$198.57	$198.55	$198.60
Purchase #7	$128.51	4.231%	$133.9473	$133.95	$133.95	$133.90
7 purchase totals =	$665.71		$712.3285	$712.33	$712.35	$712.30