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	$78.47	9.316%	$85.7803	$85.78	$85.80	$85.80
Purchase #2	$115.60	4.602%	$120.9199	$120.92	$120.90	$120.90
Purchase #3	$97.54	12.129%	$109.3706	$109.37	$109.35	$109.40
Purchase #4	$213.96	4.615%	$223.8343	$223.83	$223.85	$223.80
Purchase #5	$69.28	10.124%	$76.2939	$76.29	$76.30	$76.30
Purchase #6	$170.61	8.129%	$184.4789	$184.48	$184.50	$184.50
Purchase #7	$92.70	10.733%	$102.6495	$102.65	$102.65	$102.60
7 purchase totals =	$838.16		$903.3274	$903.32	$903.35	$903.30