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	$140.53	9.254%	$153.5346	$153.53	$153.55	$153.50
Purchase #2	$40.71	5.250%	$42.8473	$42.85	$42.85	$42.80
Purchase #3	$164.90	3.124%	$170.0515	$170.05	$170.05	$170.10
Purchase #4	$123.69	8.874%	$134.6663	$134.67	$134.65	$134.70
Purchase #5	$211.83	10.705%	$234.5064	$234.51	$234.50	$234.50
Purchase #6	$90.53	13.594%	$102.8366	$102.84	$102.85	$102.80
Purchase #7	$38.33	5.833%	$40.5658	$40.57	$40.55	$40.60
7 purchase totals =	$810.52		$879.0085	$879.02	$879.00	$879.00