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	$72.72	7.524%	$78.1915	$78.19	$78.20	$78.20
Purchase #2	$78.53	6.359%	$83.5237	$83.52	$83.50	$83.50
Purchase #3	$132.90	6.483%	$141.5159	$141.52	$141.50	$141.50
Purchase #4	$250.79	10.440%	$276.9725	$276.97	$276.95	$277.00
Purchase #5	$141.81	7.344%	$152.2245	$152.22	$152.20	$152.20
Purchase #6	$46.87	10.199%	$51.6503	$51.65	$51.65	$51.70
Purchase #7	$122.54	13.304%	$138.8427	$138.84	$138.85	$138.80
7 purchase totals =	$846.16		$922.9211	$922.91	$922.85	$922.90