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	$73.96	7.541%	$79.5373	$79.54	$79.55	$79.50
Purchase #2	$129.48	7.695%	$139.4435	$139.44	$139.45	$139.40
Purchase #3	$40.52	3.336%	$41.8717	$41.87	$41.85	$41.90
Purchase #4	$244.42	12.247%	$274.3541	$274.35	$274.35	$274.40
Purchase #5	$79.36	13.317%	$89.9284	$89.93	$89.95	$89.90
Purchase #6	$87.88	8.569%	$95.4104	$95.41	$95.40	$95.40
Purchase #7	$188.86	12.573%	$212.6054	$212.61	$212.60	$212.60
7 purchase totals =	$844.48		$933.1508	$933.15	$933.15	$933.10