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	$82.76	10.547%	$91.4887	$91.49	$91.50	$91.50
Purchase #2	$215.71	5.566%	$227.7164	$227.72	$227.70	$227.70
Purchase #3	$137.54	3.481%	$142.3278	$142.33	$142.35	$142.30
Purchase #4	$13.81	12.401%	$15.5226	$15.52	$15.50	$15.50
Purchase #5	$45.56	10.635%	$50.4053	$50.41	$50.40	$50.40
Purchase #6	$249.45	7.292%	$267.6399	$267.64	$267.65	$267.60
Purchase #7	$22.97	10.512%	$25.3846	$25.38	$25.40	$25.40
7 purchase totals =	$767.80		$820.4853	$820.49	$820.50	$820.40