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	$237.56	11.141%	$264.0266	$264.03	$264.05	$264.00
Purchase #2	$38.43	13.166%	$43.4897	$43.49	$43.50	$43.50
Purchase #3	$118.57	7.859%	$127.8884	$127.89	$127.90	$127.90
Purchase #4	$11.71	11.480%	$13.0543	$13.05	$13.05	$13.10
Purchase #5	$6.30	9.417%	$6.8933	$6.89	$6.90	$6.90
Purchase #6	$240.39	5.494%	$253.597	$253.60	$253.60	$253.60
Purchase #7	$89.35	13.162%	$101.1102	$101.11	$101.10	$101.10
7 purchase totals =	$742.31		$810.0595	$810.06	$810.10	$810.10