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	$131.60	3.648%	$136.4008	$136.40	$136.40	$136.40
Purchase #2	$99.26	3.247%	$102.483	$102.48	$102.50	$102.50
Purchase #3	$131.47	7.497%	$141.3263	$141.33	$141.35	$141.30
Purchase #4	$205.49	13.818%	$233.8846	$233.88	$233.90	$233.90
Purchase #5	$198.39	5.601%	$209.5018	$209.50	$209.50	$209.50
Purchase #6	$185.27	12.407%	$208.2564	$208.26	$208.25	$208.30
Purchase #7	$182.36	4.202%	$190.0228	$190.02	$190.00	$190.00
7 purchase totals =	$1,133.84		$1,221.8757	$1,221.87	$1,221.90	$1,221.90