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	$125.46	9.820%	$137.7802	$137.78	$137.80	$137.80
Purchase #2	$91.52	10.198%	$100.8532	$100.85	$100.85	$100.90
Purchase #3	$72.92	13.498%	$82.7627	$82.76	$82.75	$82.80
Purchase #4	$84.48	4.535%	$88.3112	$88.31	$88.30	$88.30
Purchase #5	$81.38	12.399%	$91.4703	$91.47	$91.45	$91.50
Purchase #6	$83.25	9.662%	$91.2936	$91.29	$91.30	$91.30
Purchase #7	$164.59	9.214%	$179.7553	$179.76	$179.75	$179.80
7 purchase totals =	$703.60		$772.2265	$772.22	$772.20	$772.40