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	$225.44	5.711%	$238.3149	$238.31	$238.30	$238.30
Purchase #2	$227.78	8.874%	$247.9932	$247.99	$248.00	$248.00
Purchase #3	$39.37	13.304%	$44.6078	$44.61	$44.60	$44.60
Purchase #4	$110.55	8.221%	$119.6383	$119.64	$119.65	$119.60
Purchase #5	$105.32	6.858%	$112.5428	$112.54	$112.55	$112.50
Purchase #6	$106.52	4.474%	$111.2857	$111.29	$111.30	$111.30
Purchase #7	$50.31	7.289%	$53.9771	$53.98	$54.00	$54.00
7 purchase totals =	$865.29		$928.3598	$928.36	$928.40	$928.30