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	$172.95	5.167%	$181.8863	$181.89	$181.90	$181.90
Purchase #2	$155.35	7.308%	$166.703	$166.70	$166.70	$166.70
Purchase #3	$127.94	10.109%	$140.8735	$140.87	$140.85	$140.90
Purchase #4	$79.28	3.272%	$81.874	$81.87	$81.85	$81.90
Purchase #5	$39.64	7.317%	$42.5405	$42.54	$42.55	$42.50
Purchase #6	$237.39	13.718%	$269.9552	$269.96	$269.95	$270.00
Purchase #7	$83.33	4.362%	$86.9649	$86.96	$86.95	$87.00
7 purchase totals =	$895.88		$970.7974	$970.79	$970.75	$970.90