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	$80.25	11.597%	$89.5566	$89.56	$89.55	$89.60
Purchase #2	$91.70	7.102%	$98.2125	$98.21	$98.20	$98.20
Purchase #3	$204.89	6.785%	$218.7918	$218.79	$218.80	$218.80
Purchase #4	$150.92	3.569%	$156.3063	$156.31	$156.30	$156.30
Purchase #5	$153.32	9.159%	$167.3626	$167.36	$167.35	$167.40
Purchase #6	$160.78	9.691%	$176.3612	$176.36	$176.35	$176.40
Purchase #7	$33.83	6.174%	$35.9187	$35.92	$35.90	$35.90
7 purchase totals =	$875.69		$942.5097	$942.51	$942.45	$942.60