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	$136.34	4.533%	$142.5203	$142.52	$142.50	$142.50
Purchase #2	$82.82	9.256%	$90.4858	$90.49	$90.50	$90.50
Purchase #3	$100.29	10.463%	$110.7833	$110.78	$110.80	$110.80
Purchase #4	$210.50	3.379%	$217.6128	$217.61	$217.60	$217.60
Purchase #5	$24.95	6.609%	$26.5989	$26.60	$26.60	$26.60
Purchase #6	$6.86	3.207%	$7.08	$7.08	$7.10	$7.10
Purchase #7	$203.33	9.290%	$222.2194	$222.22	$222.20	$222.20
7 purchase totals =	$765.09		$817.3005	$817.30	$817.30	$817.30