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	$37.50	6.684%	$40.0065	$40.01	$40.00	$40.00
Purchase #2	$142.30	7.633%	$153.1618	$153.16	$153.15	$153.20
Purchase #3	$184.46	3.813%	$191.4935	$191.49	$191.50	$191.50
Purchase #4	$149.97	12.520%	$168.7462	$168.75	$168.75	$168.70
Purchase #5	$126.25	3.871%	$131.1371	$131.14	$131.15	$131.10
Purchase #6	$124.72	12.432%	$140.2252	$140.23	$140.25	$140.20
Purchase #7	$85.71	11.126%	$95.2461	$95.25	$95.25	$95.20
7 purchase totals =	$850.91		$920.0164	$920.03	$920.05	$919.90