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	$122.33	6.163%	$129.8692	$129.87	$129.85	$129.90
Purchase #2	$36.78	4.573%	$38.4619	$38.46	$38.45	$38.50
Purchase #3	$186.73	10.709%	$206.7269	$206.73	$206.75	$206.70
Purchase #4	$41.27	4.507%	$43.13	$43.13	$43.15	$43.10
Purchase #5	$168.55	8.113%	$182.2245	$182.22	$182.20	$182.20
Purchase #6	$49.96	9.215%	$54.5638	$54.56	$54.55	$54.60
Purchase #7	$232.79	9.761%	$255.5126	$255.51	$255.50	$255.50
7 purchase totals =	$838.41		$910.4889	$910.48	$910.45	$910.50