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	$38.79	3.772%	$40.2532	$40.25	$40.25	$40.30
Purchase #2	$53.36	10.588%	$59.0098	$59.01	$59.00	$59.00
Purchase #3	$39.66	12.411%	$44.5822	$44.58	$44.60	$44.60
Purchase #4	$181.37	6.629%	$193.393	$193.39	$193.40	$193.40
Purchase #5	$181.65	5.457%	$191.5626	$191.56	$191.55	$191.60
Purchase #6	$148.38	12.172%	$166.4408	$166.44	$166.45	$166.40
Purchase #7	$157.59	8.281%	$170.64	$170.64	$170.65	$170.60
7 purchase totals =	$800.80		$865.8816	$865.87	$865.90	$865.90