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	$158.71	12.334%	$178.2853	$178.29	$178.30	$178.30
Purchase #2	$12.77	11.591%	$14.2502	$14.25	$14.25	$14.30
Purchase #3	$168.72	3.687%	$174.9407	$174.94	$174.95	$174.90
Purchase #4	$124.67	11.632%	$139.1716	$139.17	$139.15	$139.20
Purchase #5	$84.48	7.150%	$90.5203	$90.52	$90.50	$90.50
Purchase #6	$225.55	10.648%	$249.5666	$249.57	$249.55	$249.60
Purchase #7	$88.92	8.365%	$96.3582	$96.36	$96.35	$96.40
7 purchase totals =	$863.82		$943.0929	$943.10	$943.05	$943.20