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	$122.86	11.242%	$136.6719	$136.67	$136.65	$136.70
Purchase #2	$52.84	12.253%	$59.3145	$59.31	$59.30	$59.30
Purchase #3	$167.82	8.744%	$182.4942	$182.49	$182.50	$182.50
Purchase #4	$221.54	3.534%	$229.3692	$229.37	$229.35	$229.40
Purchase #5	$213.31	4.768%	$223.4806	$223.48	$223.50	$223.50
Purchase #6	$50.94	10.604%	$56.3417	$56.34	$56.35	$56.30
Purchase #7	$207.42	9.828%	$227.8052	$227.81	$227.80	$227.80
7 purchase totals =	$1,036.73		$1,115.4773	$1,115.47	$1,115.45	$1,115.50