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	$202.53	9.294%	$221.3531	$221.35	$221.35	$221.40
Purchase #2	$105.58	6.610%	$112.5588	$112.56	$112.55	$112.60
Purchase #3	$37.40	9.255%	$40.8614	$40.86	$40.85	$40.90
Purchase #4	$122.35	7.515%	$131.5446	$131.54	$131.55	$131.50
Purchase #5	$72.28	8.791%	$78.6341	$78.63	$78.65	$78.60
Purchase #6	$210.62	5.341%	$221.8692	$221.87	$221.85	$221.90
Purchase #7	$107.59	4.237%	$112.1486	$112.15	$112.15	$112.10
7 purchase totals =	$858.35		$918.9698	$918.96	$918.95	$919.00