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	$40.56	7.425%	$43.5716	$43.57	$43.55	$43.60
Purchase #2	$227.58	13.788%	$258.9587	$258.96	$258.95	$259.00
Purchase #3	$155.45	5.759%	$164.4024	$164.40	$164.40	$164.40
Purchase #4	$224.78	6.219%	$238.7591	$238.76	$238.75	$238.80
Purchase #5	$167.25	3.387%	$172.9148	$172.91	$172.90	$172.90
Purchase #6	$219.90	4.390%	$229.5536	$229.55	$229.55	$229.60
Purchase #7	$211.36	12.742%	$238.2915	$238.29	$238.30	$238.30
7 purchase totals =	$1,246.88		$1,346.4517	$1,346.44	$1,346.40	$1,346.60