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	$39.80	9.373%	$43.5305	$43.53	$43.55	$43.50
Purchase #2	$40.44	4.584%	$42.2938	$42.29	$42.30	$42.30
Purchase #3	$77.87	12.817%	$87.8506	$87.85	$87.85	$87.90
Purchase #4	$75.74	3.134%	$78.1137	$78.11	$78.10	$78.10
Purchase #5	$40.30	4.541%	$42.13	$42.13	$42.15	$42.10
Purchase #6	$68.51	4.443%	$71.5539	$71.55	$71.55	$71.60
Purchase #7	$165.27	10.277%	$182.2548	$182.25	$182.25	$182.30
7 purchase totals =	$507.93		$547.7273	$547.71	$547.75	$547.80