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	$25.72	8.381%	$27.8756	$27.88	$27.90	$27.90
Purchase #2	$127.97	9.731%	$140.4228	$140.42	$140.40	$140.40
Purchase #3	$74.49	12.116%	$83.5152	$83.52	$83.50	$83.50
Purchase #4	$25.88	11.544%	$28.8676	$28.87	$28.85	$28.90
Purchase #5	$125.94	12.381%	$141.5326	$141.53	$141.55	$141.50
Purchase #6	$152.88	7.674%	$164.612	$164.61	$164.60	$164.60
Purchase #7	$205.48	6.600%	$219.0417	$219.04	$219.05	$219.00
7 purchase totals =	$738.36		$805.8675	$805.87	$805.85	$805.80