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	$160.45	12.786%	$180.9651	$180.97	$180.95	$181.00
Purchase #2	$182.59	4.821%	$191.3927	$191.39	$191.40	$191.40
Purchase #3	$207.27	11.755%	$231.6346	$231.63	$231.65	$231.60
Purchase #4	$186.54	5.140%	$196.1282	$196.13	$196.15	$196.10
Purchase #5	$117.72	12.360%	$132.2702	$132.27	$132.25	$132.30
Purchase #6	$50.75	7.221%	$54.4147	$54.41	$54.40	$54.40
Purchase #7	$244.49	11.796%	$273.33	$273.33	$273.35	$273.30
7 purchase totals =	$1,149.81		$1,260.1355	$1,260.13	$1,260.15	$1,260.10