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	$241.35	11.776%	$269.7714	$269.77	$269.75	$269.80
Purchase #2	$42.71	6.534%	$45.5007	$45.50	$45.50	$45.50
Purchase #3	$72.43	8.829%	$78.8248	$78.82	$78.80	$78.80
Purchase #4	$26.83	3.463%	$27.7591	$27.76	$27.75	$27.80
Purchase #5	$30.97	4.689%	$32.4222	$32.42	$32.40	$32.40
Purchase #6	$61.39	3.127%	$63.3097	$63.31	$63.30	$63.30
Purchase #7	$20.85	4.386%	$21.7645	$21.76	$21.75	$21.80
7 purchase totals =	$496.53		$539.3524	$539.34	$539.25	$539.40