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	$137.75	5.212%	$144.9295	$144.93	$144.95	$144.90
Purchase #2	$112.34	5.419%	$118.4277	$118.43	$118.45	$118.40
Purchase #3	$64.67	8.243%	$70.0007	$70.00	$70.00	$70.00
Purchase #4	$101.78	3.391%	$105.2314	$105.23	$105.25	$105.20
Purchase #5	$168.33	5.848%	$178.1739	$178.17	$178.15	$178.20
Purchase #6	$190.58	10.154%	$209.9315	$209.93	$209.95	$209.90
Purchase #7	$85.74	5.472%	$90.4317	$90.43	$90.45	$90.40
7 purchase totals =	$861.19		$917.1264	$917.12	$917.20	$917.00