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	$220.96	13.765%	$251.3751	$251.38	$251.40	$251.40
Purchase #2	$28.41	5.129%	$29.8671	$29.87	$29.85	$29.90
Purchase #3	$85.45	6.412%	$90.9291	$90.93	$90.95	$90.90
Purchase #4	$6.30	3.218%	$6.5027	$6.50	$6.50	$6.50
Purchase #5	$52.41	13.288%	$59.3742	$59.37	$59.35	$59.40
Purchase #6	$234.38	13.247%	$265.4283	$265.43	$265.45	$265.40
Purchase #7	$150.30	11.802%	$168.0384	$168.04	$168.05	$168.00
7 purchase totals =	$778.21		$871.5149	$871.52	$871.55	$871.50