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	$250.78	10.191%	$276.337	$276.34	$276.35	$276.30
Purchase #2	$200.81	13.779%	$228.4796	$228.48	$228.50	$228.50
Purchase #3	$105.80	7.320%	$113.5446	$113.54	$113.55	$113.50
Purchase #4	$128.74	12.232%	$144.4875	$144.49	$144.50	$144.50
Purchase #5	$58.82	12.861%	$66.3848	$66.38	$66.40	$66.40
Purchase #6	$83.30	10.681%	$92.1973	$92.20	$92.20	$92.20
Purchase #7	$72.96	4.815%	$76.473	$76.47	$76.45	$76.50
7 purchase totals =	$901.21		$997.9038	$997.90	$997.95	$997.90