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	$184.76	6.294%	$196.3888	$196.39	$196.40	$196.40
Purchase #2	$63.77	6.523%	$67.9297	$67.93	$67.95	$67.90
Purchase #3	$40.54	7.714%	$43.6673	$43.67	$43.65	$43.70
Purchase #4	$110.61	10.432%	$122.1488	$122.15	$122.15	$122.10
Purchase #5	$67.52	3.531%	$69.9041	$69.90	$69.90	$69.90
Purchase #6	$243.28	9.477%	$266.3356	$266.34	$266.35	$266.30
Purchase #7	$38.58	11.775%	$43.1228	$43.12	$43.10	$43.10
7 purchase totals =	$749.06		$809.4971	$809.50	$809.50	$809.40