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	$161.36	10.863%	$178.8885	$178.89	$178.90	$178.90
Purchase #2	$99.51	10.432%	$109.8909	$109.89	$109.90	$109.90
Purchase #3	$193.84	11.370%	$215.8796	$215.88	$215.90	$215.90
Purchase #4	$230.40	3.850%	$239.2704	$239.27	$239.25	$239.30
Purchase #5	$73.67	13.636%	$83.7156	$83.72	$83.70	$83.70
Purchase #6	$168.69	6.819%	$180.193	$180.19	$180.20	$180.20
Purchase #7	$118.34	13.164%	$133.9183	$133.92	$133.90	$133.90
7 purchase totals =	$1,045.81		$1,141.7563	$1,141.76	$1,141.75	$1,141.80