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	$208.73	9.296%	$228.1335	$228.13	$228.15	$228.10
Purchase #2	$236.37	10.584%	$261.3874	$261.39	$261.40	$261.40
Purchase #3	$78.98	13.372%	$89.5412	$89.54	$89.55	$89.50
Purchase #4	$231.91	10.108%	$255.3515	$255.35	$255.35	$255.40
Purchase #5	$153.56	5.447%	$161.9244	$161.92	$161.90	$161.90
Purchase #6	$193.30	11.563%	$215.6513	$215.65	$215.65	$215.70
Purchase #7	$20.42	7.302%	$21.9111	$21.91	$21.90	$21.90
7 purchase totals =	$1,123.27		$1,233.9004	$1,233.89	$1,233.90	$1,233.90