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	$50.31	3.772%	$52.2077	$52.21	$52.20	$52.20
Purchase #2	$37.69	6.128%	$39.9996	$40.00	$40.00	$40.00
Purchase #3	$84.48	3.557%	$87.485	$87.49	$87.50	$87.50
Purchase #4	$72.94	6.853%	$77.9386	$77.94	$77.95	$77.90
Purchase #5	$124.37	5.440%	$131.1357	$131.14	$131.15	$131.10
Purchase #6	$134.83	6.815%	$144.0187	$144.02	$144.00	$144.00
Purchase #7	$246.94	3.786%	$256.2891	$256.29	$256.30	$256.30
7 purchase totals =	$751.56		$789.0744	$789.09	$789.10	$789.00