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	$88.95	13.474%	$100.9351	$100.94	$100.95	$100.90
Purchase #2	$128.58	11.258%	$143.0555	$143.06	$143.05	$143.10
Purchase #3	$225.72	7.365%	$242.3443	$242.34	$242.35	$242.30
Purchase #4	$208.29	7.550%	$224.0159	$224.02	$224.00	$224.00
Purchase #5	$181.89	12.840%	$205.2447	$205.24	$205.25	$205.20
Purchase #6	$123.71	10.473%	$136.6661	$136.67	$136.65	$136.70
Purchase #7	$19.25	6.489%	$20.4991	$20.50	$20.50	$20.50
7 purchase totals =	$976.39		$1,072.7607	$1,072.77	$1,072.75	$1,072.70