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	$86.47	5.678%	$91.3798	$91.38	$91.40	$91.40
Purchase #2	$247.54	13.113%	$279.9999	$280.00	$280.00	$280.00
Purchase #3	$135.43	7.237%	$145.2311	$145.23	$145.25	$145.20
Purchase #4	$73.94	10.236%	$81.5085	$81.51	$81.50	$81.50
Purchase #5	$89.76	12.375%	$100.8678	$100.87	$100.85	$100.90
Purchase #6	$144.51	12.419%	$162.4567	$162.46	$162.45	$162.50
Purchase #7	$135.69	4.745%	$142.1285	$142.13	$142.15	$142.10
7 purchase totals =	$913.34		$1,003.5723	$1,003.58	$1,003.60	$1,003.60