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	$13.98	11.155%	$15.5395	$15.54	$15.55	$15.50
Purchase #2	$199.83	9.332%	$218.4781	$218.48	$218.50	$218.50
Purchase #3	$28.72	10.145%	$31.6336	$31.63	$31.65	$31.60
Purchase #4	$212.87	3.130%	$219.5328	$219.53	$219.55	$219.50
Purchase #5	$36.91	7.601%	$39.7155	$39.72	$39.70	$39.70
Purchase #6	$73.91	10.502%	$81.672	$81.67	$81.65	$81.70
Purchase #7	$174.49	12.581%	$196.4426	$196.44	$196.45	$196.40
7 purchase totals =	$740.71		$803.0141	$803.01	$803.05	$802.90