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	$63.65	5.613%	$67.2227	$67.22	$67.20	$67.20
Purchase #2	$134.38	3.357%	$138.8911	$138.89	$138.90	$138.90
Purchase #3	$82.36	9.781%	$90.4156	$90.42	$90.40	$90.40
Purchase #4	$147.83	9.666%	$162.1192	$162.12	$162.10	$162.10
Purchase #5	$140.89	4.453%	$147.1638	$147.16	$147.15	$147.20
Purchase #6	$134.59	9.715%	$147.6654	$147.67	$147.65	$147.70
Purchase #7	$139.90	5.406%	$147.463	$147.46	$147.45	$147.50
7 purchase totals =	$843.60		$900.9408	$900.94	$900.85	$901.00