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	$127.90	7.411%	$137.3787	$137.38	$137.40	$137.40
Purchase #2	$64.32	11.260%	$71.5624	$71.56	$71.55	$71.60
Purchase #3	$64.39	9.422%	$70.4568	$70.46	$70.45	$70.50
Purchase #4	$186.80	4.144%	$194.541	$194.54	$194.55	$194.50
Purchase #5	$250.80	5.869%	$265.5195	$265.52	$265.50	$265.50
Purchase #6	$52.36	3.248%	$54.0607	$54.06	$54.05	$54.10
Purchase #7	$43.92	12.166%	$49.2633	$49.26	$49.25	$49.30
7 purchase totals =	$790.49		$842.7824	$842.78	$842.75	$842.90