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	$164.82	11.173%	$183.2353	$183.24	$183.25	$183.20
Purchase #2	$65.55	11.486%	$73.0791	$73.08	$73.10	$73.10
Purchase #3	$9.61	6.492%	$10.2339	$10.23	$10.25	$10.20
Purchase #4	$42.39	3.128%	$43.716	$43.72	$43.70	$43.70
Purchase #5	$5.73	7.150%	$6.1397	$6.14	$6.15	$6.10
Purchase #6	$80.50	3.835%	$83.5872	$83.59	$83.60	$83.60
Purchase #7	$78.71	9.153%	$85.9143	$85.91	$85.90	$85.90
7 purchase totals =	$447.31		$485.9055	$485.91	$485.95	$485.80