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	$218.45	7.634%	$235.1265	$235.13	$235.15	$235.10
Purchase #2	$118.69	3.646%	$123.0174	$123.02	$123.00	$123.00
Purchase #3	$37.31	7.260%	$40.0187	$40.02	$40.00	$40.00
Purchase #4	$178.89	12.572%	$201.3801	$201.38	$201.40	$201.40
Purchase #5	$83.52	7.714%	$89.9627	$89.96	$89.95	$90.00
Purchase #6	$137.43	5.178%	$144.5461	$144.55	$144.55	$144.50
Purchase #7	$151.30	5.512%	$159.6397	$159.64	$159.65	$159.60
7 purchase totals =	$925.59		$993.6912	$993.70	$993.70	$993.60