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	$120.33	13.676%	$136.7863	$136.79	$136.80	$136.80
Purchase #2	$249.41	6.455%	$265.5094	$265.51	$265.50	$265.50
Purchase #3	$157.66	8.670%	$171.3291	$171.33	$171.35	$171.30
Purchase #4	$82.81	10.535%	$91.534	$91.53	$91.55	$91.50
Purchase #5	$167.97	13.744%	$191.0558	$191.06	$191.05	$191.10
Purchase #6	$178.39	10.298%	$196.7606	$196.76	$196.75	$196.80
Purchase #7	$231.91	5.491%	$244.6442	$244.64	$244.65	$244.60
7 purchase totals =	$1,188.48		$1,297.6194	$1,297.62	$1,297.65	$1,297.60