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	$120.52	6.511%	$128.3671	$128.37	$128.35	$128.40
Purchase #2	$201.50	4.777%	$211.1257	$211.13	$211.15	$211.10
Purchase #3	$74.83	9.334%	$81.8146	$81.81	$81.80	$81.80
Purchase #4	$161.66	4.389%	$168.7553	$168.76	$168.75	$168.80
Purchase #5	$73.25	12.510%	$82.4136	$82.41	$82.40	$82.40
Purchase #6	$199.98	11.476%	$222.9297	$222.93	$222.95	$222.90
Purchase #7	$111.41	7.458%	$119.719	$119.72	$119.70	$119.70
7 purchase totals =	$943.15		$1,015.1250	$1,015.13	$1,015.10	$1,015.10