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	$246.82	10.389%	$272.4621	$272.46	$272.45	$272.50
Purchase #2	$209.85	12.864%	$236.8451	$236.85	$236.85	$236.80
Purchase #3	$152.68	10.650%	$168.9404	$168.94	$168.95	$168.90
Purchase #4	$36.78	8.109%	$39.7625	$39.76	$39.75	$39.80
Purchase #5	$143.72	5.622%	$151.7999	$151.80	$151.80	$151.80
Purchase #6	$129.97	11.218%	$144.55	$144.55	$144.55	$144.60
Purchase #7	$130.45	13.322%	$147.8285	$147.83	$147.85	$147.80
7 purchase totals =	$1,050.27		$1,162.1885	$1,162.19	$1,162.20	$1,162.20