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	$225.40	5.105%	$236.9067	$236.91	$236.90	$236.90
Purchase #2	$64.66	10.604%	$71.5165	$71.52	$71.50	$71.50
Purchase #3	$161.88	6.480%	$172.3698	$172.37	$172.35	$172.40
Purchase #4	$51.54	7.624%	$55.4694	$55.47	$55.45	$55.50
Purchase #5	$156.66	9.517%	$171.5693	$171.57	$171.55	$171.60
Purchase #6	$127.27	7.156%	$136.3774	$136.38	$136.40	$136.40
Purchase #7	$197.76	12.369%	$222.2209	$222.22	$222.20	$222.20
7 purchase totals =	$985.17		$1,066.4300	$1,066.44	$1,066.35	$1,066.50