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	$10.54	13.652%	$11.9789	$11.98	$12.00	$12.00
Purchase #2	$62.63	13.864%	$71.313	$71.31	$71.30	$71.30
Purchase #3	$212.54	4.490%	$222.083	$222.08	$222.10	$222.10
Purchase #4	$100.33	9.238%	$109.5985	$109.60	$109.60	$109.60
Purchase #5	$193.36	11.292%	$215.1942	$215.19	$215.20	$215.20
Purchase #6	$195.43	10.426%	$215.8055	$215.81	$215.80	$215.80
Purchase #7	$103.96	3.314%	$107.4052	$107.41	$107.40	$107.40
7 purchase totals =	$878.79		$953.3783	$953.38	$953.40	$953.40