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	$244.53	8.179%	$264.5301	$264.53	$264.55	$264.50
Purchase #2	$51.90	8.657%	$56.393	$56.39	$56.40	$56.40
Purchase #3	$135.72	6.293%	$144.2609	$144.26	$144.25	$144.30
Purchase #4	$136.59	3.239%	$141.0142	$141.01	$141.00	$141.00
Purchase #5	$90.43	7.731%	$97.4211	$97.42	$97.40	$97.40
Purchase #6	$161.39	5.358%	$170.0373	$170.04	$170.05	$170.00
Purchase #7	$73.71	12.497%	$82.9215	$82.92	$82.90	$82.90
7 purchase totals =	$894.27		$956.5781	$956.57	$956.55	$956.50