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	$139.59	3.816%	$144.9168	$144.92	$144.90	$144.90
Purchase #2	$108.29	3.749%	$112.3498	$112.35	$112.35	$112.30
Purchase #3	$244.56	11.746%	$273.286	$273.29	$273.30	$273.30
Purchase #4	$150.40	11.272%	$167.3531	$167.35	$167.35	$167.40
Purchase #5	$212.75	4.287%	$221.8706	$221.87	$221.85	$221.90
Purchase #6	$38.77	9.471%	$42.4419	$42.44	$42.45	$42.40
Purchase #7	$181.58	12.270%	$203.8599	$203.86	$203.85	$203.90
7 purchase totals =	$1,075.94		$1,166.0781	$1,166.08	$1,166.05	$1,166.10