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	$99.28	5.301%	$104.5428	$104.54	$104.55	$104.50
Purchase #2	$149.27	12.422%	$167.8123	$167.81	$167.80	$167.80
Purchase #3	$35.86	7.757%	$38.6417	$38.64	$38.65	$38.60
Purchase #4	$227.47	3.686%	$235.8545	$235.85	$235.85	$235.90
Purchase #5	$138.47	8.732%	$150.5612	$150.56	$150.55	$150.60
Purchase #6	$48.39	12.668%	$54.52	$54.52	$54.50	$54.50
Purchase #7	$36.80	8.456%	$39.9118	$39.91	$39.90	$39.90
7 purchase totals =	$735.54		$791.8443	$791.83	$791.80	$791.80