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	$162.58	12.206%	$182.4245	$182.42	$182.40	$182.40
Purchase #2	$146.27	3.396%	$151.2373	$151.24	$151.25	$151.20
Purchase #3	$215.44	3.398%	$222.7607	$222.76	$222.75	$222.80
Purchase #4	$208.31	12.634%	$234.6279	$234.63	$234.65	$234.60
Purchase #5	$186.55	5.444%	$196.7058	$196.71	$196.70	$196.70
Purchase #6	$75.86	11.408%	$84.5141	$84.51	$84.50	$84.50
Purchase #7	$201.75	12.675%	$227.3218	$227.32	$227.30	$227.30
7 purchase totals =	$1,196.76		$1,299.5921	$1,299.59	$1,299.55	$1,299.50