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	$92.43	8.531%	$100.3152	$100.32	$100.30	$100.30
Purchase #2	$69.81	12.430%	$78.4874	$78.49	$78.50	$78.50
Purchase #3	$248.53	4.583%	$259.9201	$259.92	$259.90	$259.90
Purchase #4	$216.63	3.410%	$224.0171	$224.02	$224.00	$224.00
Purchase #5	$69.77	13.110%	$78.9168	$78.92	$78.90	$78.90
Purchase #6	$50.37	11.812%	$56.3197	$56.32	$56.30	$56.30
Purchase #7	$115.36	4.332%	$120.3574	$120.36	$120.35	$120.40
7 purchase totals =	$862.90		$918.3337	$918.35	$918.25	$918.30