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	$236.97	8.201%	$256.4039	$256.40	$256.40	$256.40
Purchase #2	$153.48	7.249%	$164.6058	$164.61	$164.60	$164.60
Purchase #3	$7.47	8.528%	$8.107	$8.11	$8.10	$8.10
Purchase #4	$113.61	4.534%	$118.7611	$118.76	$118.75	$118.80
Purchase #5	$150.51	11.501%	$167.8202	$167.82	$167.80	$167.80
Purchase #6	$116.40	13.199%	$131.7636	$131.76	$131.75	$131.80
Purchase #7	$75.84	13.406%	$86.0071	$86.01	$86.00	$86.00
7 purchase totals =	$854.28		$933.4687	$933.47	$933.40	$933.50