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	$12.26	13.300%	$13.8906	$13.89	$13.90	$13.90
Purchase #2	$187.86	13.151%	$212.5655	$212.57	$212.55	$212.60
Purchase #3	$111.50	5.264%	$117.3694	$117.37	$117.35	$117.40
Purchase #4	$104.80	6.311%	$111.4139	$111.41	$111.40	$111.40
Purchase #5	$129.70	11.554%	$144.6855	$144.69	$144.70	$144.70
Purchase #6	$56.83	3.168%	$58.6304	$58.63	$58.65	$58.60
Purchase #7	$82.88	12.565%	$93.2939	$93.29	$93.30	$93.30
7 purchase totals =	$685.83		$751.8492	$751.85	$751.85	$751.90