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	$52.99	3.455%	$54.8208	$54.82	$54.80	$54.80
Purchase #2	$102.78	11.814%	$114.9224	$114.92	$114.90	$114.90
Purchase #3	$164.41	6.755%	$175.5159	$175.52	$175.50	$175.50
Purchase #4	$98.64	3.296%	$101.8912	$101.89	$101.90	$101.90
Purchase #5	$219.86	9.678%	$241.1381	$241.14	$241.15	$241.10
Purchase #6	$33.37	5.360%	$35.1586	$35.16	$35.15	$35.20
Purchase #7	$83.58	12.308%	$93.867	$93.87	$93.85	$93.90
7 purchase totals =	$755.63		$817.3140	$817.32	$817.25	$817.30