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	$144.83	9.640%	$158.7916	$158.79	$158.80	$158.80
Purchase #2	$37.83	6.609%	$40.3302	$40.33	$40.35	$40.30
Purchase #3	$186.87	8.696%	$203.1202	$203.12	$203.10	$203.10
Purchase #4	$160.44	3.354%	$165.8212	$165.82	$165.80	$165.80
Purchase #5	$197.43	12.634%	$222.3733	$222.37	$222.35	$222.40
Purchase #6	$157.41	12.127%	$176.4991	$176.50	$176.50	$176.50
Purchase #7	$39.36	11.500%	$43.8864	$43.89	$43.90	$43.90
7 purchase totals =	$924.17		$1,010.8220	$1,010.82	$1,010.80	$1,010.80