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	$39.69	4.168%	$41.3443	$41.34	$41.35	$41.30
Purchase #2	$193.98	8.177%	$209.8417	$209.84	$209.85	$209.80
Purchase #3	$144.56	8.259%	$156.4992	$156.50	$156.50	$156.50
Purchase #4	$65.90	9.297%	$72.0267	$72.03	$72.05	$72.00
Purchase #5	$56.42	11.500%	$62.9083	$62.91	$62.90	$62.90
Purchase #6	$149.34	6.869%	$159.5982	$159.60	$159.60	$159.60
Purchase #7	$90.82	8.112%	$98.1873	$98.19	$98.20	$98.20
7 purchase totals =	$740.71		$800.4057	$800.41	$800.45	$800.30