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	$212.32	4.776%	$222.4604	$222.46	$222.45	$222.50
Purchase #2	$166.85	11.759%	$186.4699	$186.47	$186.45	$186.50
Purchase #3	$39.29	9.275%	$42.9341	$42.93	$42.95	$42.90
Purchase #4	$164.49	9.637%	$180.3419	$180.34	$180.35	$180.30
Purchase #5	$101.25	4.664%	$105.9723	$105.97	$105.95	$106.00
Purchase #6	$87.76	13.361%	$99.4856	$99.49	$99.50	$99.50
Purchase #7	$98.57	6.268%	$104.7484	$104.75	$104.75	$104.70
7 purchase totals =	$870.53		$942.4126	$942.41	$942.40	$942.40