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	$49.86	11.768%	$55.7275	$55.73	$55.75	$55.70
Purchase #2	$109.71	7.135%	$117.5378	$117.54	$117.55	$117.50
Purchase #3	$91.80	12.779%	$103.5311	$103.53	$103.55	$103.50
Purchase #4	$67.99	9.658%	$74.5565	$74.56	$74.55	$74.60
Purchase #5	$88.61	13.571%	$100.6353	$100.64	$100.65	$100.60
Purchase #6	$94.54	9.398%	$103.4249	$103.42	$103.40	$103.40
Purchase #7	$150.90	6.354%	$160.4882	$160.49	$160.50	$160.50
7 purchase totals =	$653.41		$715.9013	$715.91	$715.95	$715.80