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	$241.92	6.200%	$256.919	$256.92	$256.90	$256.90
Purchase #2	$35.80	10.261%	$39.4734	$39.47	$39.45	$39.50
Purchase #3	$78.58	13.552%	$89.2292	$89.23	$89.25	$89.20
Purchase #4	$145.83	12.849%	$164.5677	$164.57	$164.55	$164.60
Purchase #5	$34.34	8.470%	$37.2486	$37.25	$37.25	$37.20
Purchase #6	$213.97	6.662%	$228.2247	$228.22	$228.20	$228.20
Purchase #7	$79.82	6.772%	$85.2254	$85.23	$85.25	$85.20
7 purchase totals =	$830.26		$900.8880	$900.89	$900.85	$900.80