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	$240.41	12.466%	$270.3795	$270.38	$270.40	$270.40
Purchase #2	$220.41	4.288%	$229.8612	$229.86	$229.85	$229.90
Purchase #3	$156.82	6.228%	$166.5867	$166.59	$166.60	$166.60
Purchase #4	$246.78	9.595%	$270.4585	$270.46	$270.45	$270.50
Purchase #5	$27.90	9.487%	$30.5469	$30.55	$30.55	$30.50
Purchase #6	$57.25	3.610%	$59.3167	$59.32	$59.30	$59.30
Purchase #7	$161.78	11.679%	$180.6743	$180.67	$180.65	$180.70
7 purchase totals =	$1,111.35		$1,207.8238	$1,207.83	$1,207.80	$1,207.90